 Many more gene sequences are known than protein structures . Further , the set of solved structures is biased toward proteins that can be easily subjected to the conditions required in X @-@ ray crystallography , one of the major structure determination methods . In particular , globular proteins are comparatively easy to crystallize in preparation for X @-@ ray crystallography . Membrane proteins , by contrast , are difficult to crystallize and are underrepresented in the PDB . Structural genomics initiatives have attempted to remedy these deficiencies by systematically solving representative structures of major fold classes . Protein structure prediction methods attempt to provide a means of generating a plausible structure for proteins whose structures have not been experimentally determined . 
 Many more gene sequences are known than protein structures . Further , the set of solved structures is biased toward proteins <a href='null_relcl' title='1'><mark>that</mark></a>can be easily subjected to the conditions required in X @-@ ray crystallography , one of the major structure determination methods . In particular , globular proteins <a href='drop_aux' title='2'><mark>are</mark></a>comparatively easy to crystallize in preparation for X @-@ ray crystallography . Membrane proteins , by contrast , <a href='drop_aux' title='3'><mark>are</mark></a>difficult to crystallize and <a href='drop_aux' title='4'><mark>are</mark></a>underrepresented in the PDB . Structural genomics initiatives <a href='been_done' title='5'><mark>have</mark></a> attempted to remedy these deficiencies by systematically solving representative structures of major fold classes . Protein structure prediction methods attempt to provide a means of generating a plausible structure for proteins whose structures have <a href='negative_concord' title='6'><mark>not</mark></a><a href='negative_concord' title='7'><mark>been</mark></a> experimentally determined . 
Many more gene sequences r known den protein structures . Further , da set of solved structures is biased toward proteins can be easily subjected to the conditions required in X @-@ ray crystallography , one of the major structure determination methods . In particular , globular proteins comparatively easy to crystallize in preparation fir X @-@ ray crystallography . Membrane proteins , by contrast , difficult to crystallize and underrepresented in the PDB . Structural genomics initiatives done attempted to remedy these deficiencies by systematically solving representative structures of major fold classes . Protein structure prediction methods attempt to provide a means of generating a plausible structure fa proteins whose structures have ain't experimentally determined .