 The chief characteristic of proteins that also allows their diverse set of functions is their ability to bind other molecules specifically and tightly . The region of the protein responsible for binding another molecule is known as the binding site and is often a depression or " pocket " on the molecular surface . This binding ability is mediated by the tertiary structure of the protein , which defines the binding site pocket , and by the chemical properties of the surrounding amino acids ' side chains . Protein binding can be extraordinarily tight and specific ; for example , the ribonuclease inhibitor protein binds to human angiogenin with a sub @-@ femtomolar dissociation constant ( < 10 − 15 M ) but does not bind at all to its amphibian homolog onconase ( > 1 M ) . Extremely minor chemical changes such as the addition of a single methyl group to a binding partner can sometimes suffice to nearly eliminate binding ; for example , the aminoacyl tRNA synthetase specific to the amino acid valine discriminates against the very similar side chain of the amino acid isoleucine . 
 The chief characteristic of proteins <a href='null_relcl' title='1'><mark>that</mark></a>also <a href='uninflect' title='2'><mark>allows</mark></a> their diverse set of functions is their ability to bind other molecules specifically and tightly . The region of the protein responsible for binding another molecule is known as the binding site and <a href='drop_aux' title='3'><mark>is</mark></a>often a depression or " pocket " on the molecular surface . This binding ability is mediated by the tertiary structure of the protein , which <a href='uninflect' title='4'><mark>defines</mark></a> the binding site pocket , and by the chemical properties of the surrounding amino acids <a href='null_genetive' title='5'><mark>'</mark></a>side chains . Protein binding can be extraordinarily tight and specific ; for example , the ribonuclease inhibitor protein binds to human angiogenin with a sub @-@ femtomolar dissociation constant ( < 10 − 15 M ) but <a href='uninflect' title='6'><mark>does</mark></a> not bind at all to its amphibian homolog onconase ( > 1 M ) . Extremely minor chemical changes such as the addition of a single methyl group to a binding partner can sometimes suffice to nearly eliminate binding ; for example , the aminoacyl tRNA synthetase specific to the amino acid valine <a href='uninflect' title='7'><mark>discriminates</mark></a> against the very similar side chain of the amino acid isoleucine . 
The chief characteristic of proteins also allow their diverse set of functions is their ability to bind other molecules specifically and tightly . The region of the protein responsible for binding another molecule is known as da binding site and often a depression or " pocket " on the molecular surface . This binding ability is mediated by the tertiary structure of tdaprotein , which define the binding site pocket , and by the chemical properties of thdaurrounding amino acids  side chains . Protein binding can be extraordinarily tight and specific ; for example , thedabonuclease inhibitor protein binds to human angiogenin with a sub @-@ femtomolar dissociation constant ( < 10 − 15 M ) but do not bind at alll to its amphibian homolog onconase ( > 1 M ) . Extremely minor chemical changes such as the addition of a single methyl group to a binding partner can sometimes suffice to nearly eliminate binding ; for example , the aminoacyl tRNA synthetase specific to the amino acid valine discriminate against the day similar side chain of the amino acid isoleucine .