Method for treating and preventing alzheimer&#39;s disease
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Grant No. 1-R01AG 10002-03 awarded by the National Institutes of Health. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to treatment and prevention of Alzheimer&#39;s disease. 
     BACKGROUND OF THE INVENTION 
     Alzheimer&#39;s disease is the most prevalent form of senile dementia. Epidemological studies suggest that 25-50% of all people in their 80&#39;s have Alzheimer&#39;s disease. There are about 4 million cases in the United States alone. Generally, the first symptom of Alzheimer&#39;s disease is memory loss, followed by a decline in reasoning ability and reduced use of speech. Behavioral disorders are also often present. The deterioration appears to be irreversible, and eventually leads to death. There is no effective treatment currently available. 
     A common feature of Alzheimer&#39;s disease and other neurodegenerative diseases is the accumulation of fibrous proteinaceous structures known as neurofibrillary tangles and senile plaques. Neurofilament (NF) protein is the main constituent of neurofibrillary tangles. NF proteins consist of three subunits based on molecular weight: high (NF-H), medium (NF-M) and low (NF-L). NF proteins form filaments via coiled-coil interactions between the structurally conservative rod sequences of NF-H, NF-M and NF-L. These filaments can give rise to neurofibrillary tangles when the NF protein is hyper-phosphorylated. β-amyloid, a protein containing about 42 amino acids, is the major component of senile plaque. β-amyloid can aggregate, giving rise to the plaques. 
     Many studies have shown that aluminum is found in neurofibrillary tangles and senile plaques. Aluminum can complex with β-amyloid or neurofilament protein. In addition, certain epidemiological studies indicate a link between aluminum in water supplies and the incidence of Alzheimer&#39;s disease. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a safe, effective, easy and inexpensive method for treating or preventing Alzheimer&#39;s disease. 
     It is yet another object of the invention to provide a method for treating or preventing Alzheimer&#39;s disease which does not involve an invasive procedure. 
     It is yet another object of the invention to provide a simple method for treating or preventing Alzheimer&#39;s disease such as administering a pill, administering an injection or inserting an implant. 
     Still another object of the invention is to treat or prevent Alzheimer&#39;s disease by administering a silicon compound which inhibits interaction between aluminum and β-amyloid or neurofilament protein, so as to reduce or reverse formation of neurofibrillary tangles and/or senile plaques. 
     According to the invention, a method for treating or preventing Alzheimer&#39;s disease in a mammal is provided. A silicon compound is provided for inhibiting interaction between aluminum and β-amyloid or neurofilament protein. The silicon compound is administered to a mammal in need of such treatment to cause this inhibition to occur. 
     The silicon compound can be, e.g., a salt, e.g., sodium silicate, sodium metasilicate or silicon tetra acetate, an acid, e.g., silicic acid, an oxide, or combinations thereof. 
     In certain embodiments, the silicon compound inhibits interaction between aluminum and the neurofilament protein so as to at least partially prevent formation of, or to at least partially reverse a formed, neurofibrillary tangle. In other embodiments, the silicon compound inhibits interaction between aluminum and β-amyloid so as to at least partially prevent, or to at least partially reverse a formed, senile plaque. 
     Variations of this method of this invention include administering the silicon compound prior to formation of a neurofibrillary tangle or a senile plaque, administering the silicon compound subsequent to formation of a neurofibrillary tangle or a senile plaque, and administering the silicon compound to a human. 
     Another aspect of the invention is a method for treating or preventing Alzheimer&#39;s disease in a mammal in which a silicon compound for at least partially preventing a neurofibrillary tangle or a senile plaque is provided. The silicon compound is administered to a mammal in need of such treatment to cause this prevention to occur. 
     Yet another aspect of the invention is a therapeutic silicon compound in a dosage form and concentration suitable for treating or preventing Alzheimer&#39;s disease in a mammal in need of such treatment, the silicon compound being effective to inhibit interaction between aluminum and β-amyloid or neurofilament protein. 
     The above and other objects, features, and advantages of the present invention will be better understood from the following specification when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts the amino acid sequence of a 17 amino acid peptide from the human neurofilament mid-sized subunit protein (NF-M17) (Seq. ID No. 1). 
     FIG. 2 depicts three phosphorylated derivatives (Seq. ID Nos. 2, 3 and 4) of the NF-M17 peptide (Seq. ID No. 1) shown in FIG. 1. 
     FIG. 3 depicts circular dichroic (CD) spectra of NF-M17 (Seq. ID No. 1) resulting from titration with Al 3+   and SiO 4   4- . 
     FIG. 4 depicts CD spectra of NF-M17 Ser 6  P (Seq. ID No. 2) resulting from titration with Al 3+   and SiO 4   4- . 
     FIG. 5 depicts CD spectra of NF-M17 Ser 11  P (Seq. ID No. 3) resulting from titration with Al 3+   and SiO 4   4- . 
     FIG. 6 depicts CD spectra of NF-M17 Ser 6  PSer 11  p (Seq. ID No. 4) resulting from titration with Al 3+   and SiO 3   4- . 
     FIG. 7 depicts the amino acid sequence of rat A42 β-amyloid (Seq. ID No. 5). 
     FIG. 8 depicts CD spectra of rat A42 β-amyloid (Seq. ID No. 5) resulting from titration with Al 3+   and SiO 4   4- . 
    
    
     DETAILED DESCRIPTION 
     This invention provides a method for treating or preventing Alzheimer&#39;s disease in a mammal. A silicon compound is provided which inhibits interaction between aluminum and β-amyloid or neurofilament protein. The silicon compound is administered to a mammal in need of such treatment to cause this inhibition to occur. 
     Alzheimer&#39;s disease is a neurodegenerative condition which is meant to include the presence of cerebrocortical neurofibrillary tangles and/or senile plaques. Treating Alzheimer&#39;s disease is meant to include preventing, arresting, altering, and/or reversing formation of neurofibrillary tangles and/or senile plaques. By mammals is meant human as well as non-human mammals. 
     A silicon compound is meant to include any chemical species which contains silicon. Silicon compounds include, e.g., acids, salts and oxides. Preferably, the silicon compound is water soluble. By water soluble is meant a compound readily soluble in water at concentrations of mg/liter. A preferred acid is silicic acid, H 4  SiO 4 , which is a very weak acid, losing its first proton at a pKa of 9.6. The solubility of silicic acid in water or blood ranges from about 1.4 to about 2.2 mM. Free aluminum cations, Al 3+   can bind to silicic acid to yield the dialyzable species, AlOSi(OH) 3   2+ , which, under physiological conditions results in hydroxyaluminosilicate. Preferably, a silicic acid concentration of about 100 μm or greater is used to complex aluminum. Such complexing renders the aluminum unreactive in a variety of physiological environments. Silicic acid is capable of binding to aluminum already bound to neurofibrillary tangles and/or β-amyloid and extracting it, causing solubilization of the precipitated protein or peptide. 
     Examples of silicon salts include sodium silicate, e.g., 2:1 or 3:1, sodium metasilicate and silicon tetra acetate. Preferably, soluble silicon salts are used. Free aluminum cations, Al 3+   can bind to the silicon salts to yield aluminum silicates. Silicon salts can also bind to neurofibrillary tangles and/or β-amyloid and extract it, causing solubilization of the precipitated protein or peptide. Silicon salts are preferred in this invention. 
     The silicon compound of this invention is able to inhibit interaction between aluminum and β-amyloid or neurofilament protein. The term inhibit interaction is meant to include inhibition which occurs either before or after the aluminum complexes with β-amyloid or neurofilament protein. For example, the silicon compound can complex with free aluminum, thereby preventing free aluminum from interacting with β-amyloid or neurofilament proteins. In other embodiments, the silicon compound can complex with aluminum that is already bound to β-amyloid or neurofilament protein, thereby removing the aluminum from the β-amyloid or neurofilament proteins. Inhibition includes partial or complete inhibition. 
     The silicon compound is administered so as to treat or prevent the formation of neurofibrillary tangles and/or senile plaques. In persons with Alzheimer&#39;s disease, the β-amyloid and neurofilament proteins found in the senile plaques and neurofibrillary tangles are generally phosphorylated and complexed with aluminum, and assume a β-sheet structure. Peri, D., in &#34;Metal Ions in Biological Systems,&#34; Vol. 24, eds. Sigel &amp; Sigel, Marcel Dekker Ins., N.Y. (1988), pp. 259-283. It is the B-sheet structure which causes these proteins to become insoluble and to precipitate out, thereby giving rise to the tangles and plaques. 
     Examples 1 and 2 illustrate that a silicon compound can reverse the structural alterations that result from the addition of aluminum to neurofilament protein (NF-M17) (Seq. ID No. 1) and β-amyloid (Seq. ID No. 5). β-amyloid (Seq. ID No. 5) and neurofilament (NF-M17) protein (Seq. ID No. 1) each normally exhibit a partial α-helical structure. Upon the addition of aluminum, β-sheet structures are formed. If a silicon compound is also added, the proteins are transformed back to their original partial α-helical structure. These results were obtained for both phosphorylated and non-phosphorylated proteins. If citrate is added instead of a silicon compound, The proteins are not transformed back to their original structure. 
     Administration of the silicon compound can be accomplished by any method which allows the silicon compound to reach its target. By target is meant the place where the silicon compound is able to inhibit interaction between aluminum and β-amyloid or neurofilament proteins. This inhibition can occur before or after the aluminum complexes with the β-amyloid or neurofilament proteins. Examples of targets include the gastrointestinal tract, the blood stream and the brain. 
     The administration methods include, e.g., injection, deposition, implantation, suppositories, oral ingestion, inhalation, topical administration, or any other method of administration where access to the target by the silicon compound is obtained. Injections can be, e.g., intravenous, intradermal, subcutaneous, intramuscular or intraperitoneal. Implantation includes inserting implantable drug delivery systems, e.g., microspheres, hydrogels, polymeric reservoirs, cholesterol matrices, polymeric systems, e.g., matrix erosion and/or diffusion systems and non-polymeric systems, e.g., compressed, fused or partially fused pellets. Suppositories include glycerin suppositories. Oral ingestion doses can be enterically coated. Inhalation includes administering the silicon compound with an aerosol in an inhalator, either alone or attached to a carrier that can be absorbed. 
     The silicon compound can be suspended in a liquid, e.g., in dissolved form or colloidal form. The liquid can be a solvent, partial solvent or non-solvent. In many cases water or an organic liquid can be used. 
     Administration of the silicon compound can be alone or in combination with other therapeutic agents. In certain embodiments, the silicon compound can be combined with a suitable carrier, incorporated into a liposome, or incorporated into a polymer release system. Silicon compounds have been demonstrated to be biocompatible. Hench et al., in &#34;Silicon Biochemistry,&#34; Ciba Foundation Symposium #121, eds. Everst &amp; O&#39;Conner, John Wiley &amp; Sons (1988). 
     In certain embodiments of the invention, the administration can be designed so as to result in sequential exposures to the agent over some time period, e.g., hours, days, weeks, months or years. This can be accomplished by repeated administrations of the silicon compound by one of the methods described above, or alternatively, by a controlled release delivery system in which the silicon compound is delivered to the mammal over a prolonged period without repeated administrations. Administration of such a system can be, e.g., by long acting oral dosage forms, bolus injections, transdermal patches and sub-cutaneous implants. Maintaining a fairly constant level of the silicon compound is preferred so as to allow for scavenging aluminum throughout the body and promoting its excretion via the kidney and bowel. Avoiding short-term elevated levels of silicon is preferred in order to minimize the precipitation of silicate kidney stones in the presence of high non-physiological levels of silicon compounds. 
     The silicon compound can be administered prior to or subsequent to neurofibrillary tangle and/or senile plaque formation. In certain embodiments, the silicon compound is administered to persons who have a family history of Alzheimer&#39;s disease, or who have a genetic predisposition for the disease. In other embodiments, the silicon compound is administered to persons who have reached a particular age and who therefore are more likely to get the disease. In yet other embodiments, the silicon compound is administered to persons who exhibit either early or advanced symptoms of the disease. The silicon compound can also be administered to persons as a preventive measure. 
     The silicon compound is administered to the mammal in a therapeutically effective amount. By therapeutically effective amount is meant that amount which is capable of at least partially preventing or reversing neurofibrillary tangle and/or plaque formation. A therapeutically effective amount can be determined on an individual basis and will be based, at least in part, on consideration of the species of mammal, the mammal&#39;s size, the silicon compound used, the type of delivery system used, the time of administration relative to tangle or plaque formation, and whether a single, multiple, or controlled release dose regimen is employed. A therapeutically effective amount can be determined by one of ordinary skill in the art employing such factors and using no more than routine experimentation. 
     Preferably, the concentration of the silicon compound is at a dose of about 0.1 m moles/liter to about 50 m moles/liter. Most preferably the dose is about 0.5 m moles/liters to about 5.0 m moles/liter. The specific concentration partially depends upon the particular silicon compound used, as some are more effective than others. The dosage concentration of the silicon compound that is actually administered is dependent at least in part upon the final concentration that is desired at the site of action, the method of administration, the efficacy of the particular silicon compound, the longevity of the particular silicon compound, and the timing of administration relative to the formation of the tangles and/or plaques. Preferably, the dosage form is such that it does not substantially deleteriously affect the mammal. The dosage can be determined by one of ordinary skill in the art employing such factors and using no more than routine experimentation. 
     The invention also includes a therapeutic silicon compound in a dosage form and concentration suitable for treating or preventing Alzheimer&#39;s disease in a mammal in need of such treatment, the silicon compound being effective to interfere with interaction between aluminum and β-amyloid or neurofilament protein. 
     EXAMPLES 
     Example 1 
     β-Sheet Formation of Phosphorylated and Non-Phosphorylated Neurofilament Mid-Sized Protein (NF-M17) by the Addition of Al 3+   and Reversibility by the Addition of Silicate 
     This example illustrates that the partial α-helical structure of phosphorylated and non-phosphorylated 17 amino acid fragments of the human neurofilament mid-sized protein (NF-M17) (Seq. ID No. 1) forms β-sheets upon the addition of Al 3+ , and that these β-sheets are substantially transformed back to the original partial α-helical structure upon the addition of SiO 4  hu 4-. 
     Peptides containing a seventeen amino acid region of the human neurofilament mid-sized subunit protein (NF-M17) were synthesized as previously described (Hollosi et al., J. Mol. Biol., 223:673-682 (1992)). FIG. 1 shows the sequence of the NF-M17 peptide (Seq. ID No. 1). After synthesis of the 17 amino acid fragment, the serines, at amino acid residue positions 6 and 11, were phosphorylated using the poly-phosphoric acid method reported by Otvos et al., J. Chromatogr. 512:265-272 (1990). The reaction was allowed to proceed for 2-3 days, after which time the reaction was neutralized and the phosphorylated products and starting material were separated using HPLC. FIG. 2 shows the three phosphorylated peptides that were produced, NF-M17 Sep 6  P (Seq. ID No. 2), NF-M17 Ser 11  P (Seq. ID No. 3) and NF-M17 Ser 6  PSer 11  P (Seq. ID No. 4). 
     2,2,2-trifluorethanol (TFE) (NMR grade) and aluminum nonahydrate were obtained from Aldrich, Milwaukee, Wis., sodium silicate was obtained from Johnson Matthey Catalog Corporation, Ward Hill, Mass. Circular dichroic (CD) spectra were acquired using a J-Y Mark V Circular Dicrograph, I.S.A. Jobin Yvon, Longjumeau, France. 
     For the CD titrations the peptides were dissolved in TFE to a concentration between 0.4-0.18 mg/ml. The Al 3+    solutions (33 or 36 mM) were prepared in TFE, and Na 4  SiO 4  was dissolved in water (136 mM). Initial spectra contained only peptide. Incremental additions of Al 3+   solution were made until 8 or 16 molar equivalents of metal ion were added to the peptide. Once the maximum conformational change was reached, SiO 4   4-   was titrated into the curvette. Additions were made as increments of peptide molar equivalents and did not exceed 32 equivalents. The conformational influence of each addition was monitored by CD. 
     A conformational transition of the non-phosphorylated MF-17 peptide (Seq. ID No. 1) from partially α-helical structure to one that contained B-sheet upon addition of Al 3+   was observed. Continued addition of Al 3+   resulted in precipitation of the peptide. These results are in agreement with previous studies by Hollosi et al., J. Mol. Biol. 223:673-682 (1992). The addition of SiO 4   4-   resulted in a CD spectrum similar to the initial partially α-helical structure. 
     The reversibility of the NF-M17/Al 3+   titration is shown in FIG. 3. The NF-M17 peptide (Seq. ID No. 1) was titrated with 16 molar equivalents of Al 3+   beginning at 2 equivalents. The initial curve (curve a) showed a peak at 190 nm and a trough at 204 nm with a shoulder at 220 nm. Each addition of Al 3+   resulted in a gradual &#34;shallowing&#34; of the deep trough and a deepening of the shoulder, a curve characteristic of a B-sheet, curve b. With each addition of SiO 4   4- , the curve gradually returned to its original shape. No significant change was noted with the first few titration points, however, when the titration approached equal molar quantities of SiO 4   4-   and Al 3+ , significant changes were noted. A spectrum similar to the initial one was observed, curve c. Twelve hours later, the same spectrum was obtained. As a control experiment, the NF-M17 peptide was titrated with just SiO 4   4-   ion to see if this had any effect on The native spectrum. Minor changes were observed: a slight rise in the baseline from 0 degrees and an increase in the peak intensity at 195 nm. These results may imply an increase in random coil content, although the overall shape of the curve was very similar to that of NF-M17 with nothing added. 
     Titrations were also done with the NF-M17 phosphorylated derivatives. NF-M17 Ser 6  P (Seq. ID No. 2), NF-M17 Ser 11  P (Seq. ID No. 3), and NF-M17 Ser 6  PSer 11  P (Seq. ID No. The presence of phosphate groups attached to the peptides induces much stronger binding to aluminum. The negative PO 4   3-   ion binds to the positively charged Al 3+   ion. The results of the reversibility titration for NF-M17 Ser 6  P peptide (Seq. ID No. 2) are illustrated in FIG. 4. The initial spectrum is shown as curve a. This peptide was converted to a β-sheet with 4 molar equivalents of Al 3+   (curve b). At equal concentrations of SiO 4   4-   and Al 3+   the peptide spectrum began to resemble the original spectrum but the 195 nm trough was not as deep. Twice as much SiO 4   4-   as Al 3  +  resulted in a spectrum which had a shallower shoulder at 220 nm and a deeper trough at 204 nm (curve c). 
     Titration of the NF-M17 Ser 11  P peptide (Seq. ID No. 3) is shown in FIG. 5. The initial spectrum is shown as a curve a. After 16 molar equivalents of Al 3+   the metal ion titration was complete, curve b. Reversibility of the Al 3+   effects required only equal molar quantities of SiO 4   4-   ion, curve c. These solution conditions resulted in a spectrum with more random character than the original spectrum. 
     The NF-M17 Ser 6  PSer 11  P peptide (Seq. ID No. 4) as shown in FIG. 6, curve a, was titrated with 8 molar equivalents of Al 3+ , shown in curve b. It required twice as much SiO 4   4-   ion to obtain a spectrum, curve c, which resembled the lone peptide. Although all of these titrations gave a more random coil-like spectrum, they were much more similar to the initial peptide spectrum than to that of the Al 3+  bound species. 
     Example 2 
     β-Sheet Formation of β-Amyloid A42 Polypeptide by the Addition of Al 3+   and Reversibility by the Addition of Silicate 
     This example illustrates that the partial α-helical structure of rat A42 β-amyloid protein (Seq. ID No. 5) forms β-sheets upon the addition of Al 3+   and that these β-sheets are transformed back to the original partial α-helical structure upon the addition of SiO 4   4- . The titration of A42 β-amyloid protein (Seq. ID No. 5) from rat, shown in FIG. 7, was performed with a 0.39 mg/mL solution; the solvent was TFE. The Al 3+   solution (41.6 mM) was prepared in TFE, and the Na 4  SiO 4  was dissolved in water (138 mM). The initial CD spectrum examined the conformation of protein only; incremental additions of Al 3+   solution (4.25 μL/molar equivalent) were made until 4 molar equivalents of metal ion were reached. After a conformational change was noted as monitored by CD, SiO 4   4-  (1.28 μL/molar equivalent) was titrated into the curvette until the CD spectrum approximated that of the original. This point was reached at a 1:1 ratio of Al 3+  :SiO 4   4- . 
     The results of the titration of the rat A42 β-amyloid protein (Seq. ID No. 5) are shown in FIG. 8. A42 in TFE without Al 3+   or SiO 4   -   is shown in curve a. This curve demonstrates a partial α-helical structure. Upon addition of 2 molar equivalents of Al 3+   the [Θ] 220  increased, indicating the formation of β-sheets (curve b). On addition of 4 equivalents of Al 3+   the curve (curve c) remained identical to that of curve b. Two mole equivalents of SiO 4   4-   added to the solution (curve d) caused no change in structure. However, addition of 4 equivalents of SiO 4   4-   produced curve e. Thus, a reverse of the effect of Al 3+   was brought about by the addition of SiO 4   4- . The A42 β-amyloid protein, which was transformed into β-sheets by the addition of Al 3+   was transformed into its initial conformation by the addition of SiO 4   4- . 
     Example 3 
     Treating Alzheimer&#39;s Disease in a Human 
     This example illustrates a method for treating Alzheimer&#39;s disease in a human with a silicon compound which inhibits interaction between aluminum and β-amyloid, and aluminum and neurofilament protein. The patient is given sodium silicate orally, in the form of a pill, once a day. The dose concentration per day is 4.0 m moles/liter. Administration is carried out for a period of six months. This treatment interferes with further development of neurofibrillary tangles and senile plaques. 
     Those skilled in the art will be able to ascertain, using no more than routine experimentation, many equivalents of the specific embodiments of the invention described herein. These and all other equivalents are intended to be encompassed by the following claims. 
     
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SEQUENCE LISTING                                                          
(1) GENERAL INFORMATION:                                                  
(iii) NUMBER OF SEQUENCES: 5                                              
(2) INFORMATION FOR SEQ ID NO:1:                                          
(i) SEQUENCE CHARACTERISTICS:                                             
(A) LENGTH: 17 amino acids                                                
(B) TYPE: amino acid                                                      
(D) TOPOLOGY: linear                                                      
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                   
GluGluLysGlyLysSerP roValProLysSerProValGluGluLys                         
151015                                                                    
Gly                                                                       
(2) INFORMATION FOR SEQ ID NO:2:                                          
(i) SEQUENCE CHARACTERISTICS:                                             
(A) LENGTH: 17 amino acids                                                
(B) TYPE: amino acid                                                      
(D) TOPOLOGY: linear                                                      
(ix) FEATURE:                                                             
(A) NAME/KEY: serine is phosphorylated                                    
(B) LOCATION: 6                                                           
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                   
GluGluLysGlyLysSerProValProLysSerProValGluGluLys                          
1510 15                                                                   
Gly                                                                       
(2) INFORMATION FOR SEQ ID NO:3:                                          
(i) SEQUENCE CHARACTERISTICS:                                             
(A) LENGTH: 17 amino acids                                                
(B) TYPE: amino acid                                                      
(D) TOPOLOGY: linear                                                      
(ix) FEATURE:                                                             
(A) NAME/KEY: serine is phosphorylated                                    
(B) LOCATION: 11                                                          
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                   
GluGluLysGlyLysS erProValProLysSerProValGluGluLys                         
151015                                                                    
Gly                                                                       
(2) INFORMATION FOR SEQ ID NO:4:                                          
(i) SEQUENCE CHARACTERISTICS:                                             
(A) LENGTH: 17 amino acids                                                
(B) TYPE: amino acid                                                      
( D) TOPOLOGY: linear                                                     
(ix) FEATURE:                                                             
(A) NAME/KEY: serines are phosphorylated                                  
(B) LOCATION: 6 and 11                                                    
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                   
GluGluLysGlyLysSerProValProLysSerProValGluGluLys                          
1510 15                                                                   
Gly                                                                       
(2) INFORMATION FOR SEQ ID NO:5:                                          
(i) SEQUENCE CHARACTERISTICS:                                             
(A) LENGTH: 42 amino acids                                                
(B) TYPE: amino acid                                                      
(D) TOPOLOGY: linear                                                      
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                   
AspAlaGluPheGlyHisAspSerGlyProGluValArgHisGlnLys                          
 151015                                                                   
LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle                          
202530                                                                    
 GlyLeuMetValGlyGlyValValIleAla                                           
3540