I investigate the structure of protein energy landscapes, symmetries of three-dimensional structures as key factors governing the shape of protein morphospace. Proteins, like organisms, exhibit a non-uniform distribution of present forms. Proteins can be divided into different sized groups of individual forms according to their fold (topology), characterized by secondary structure elements (a helix and b sheet) and their arrangement. Despite the fact that only a small percentage of existing protein structures has been solved experimentally and the representation of form in structural databases is highly biased, it has been repeatedly shown that the distribution of individual protein structures between folds is far from uniform (Chothia, 1986, Richardson, 1981, Ptitsyn, and Finkelstein, 1980). Out of the 564 folds represented in SCOP (structural protein classification) ten folds account for one third of the structures in PDB (Protein Data Bank) (Brenner, et al., 1997, Orengo, et al., 1994, Zhang and DeLisi?, 2001). These folds, also known as superfolds(Orengo, et al., 1994, Salem, et al., 1999), include globin, updown, trefoil, Tim barrel, OB roll, doubly wound, immunoglobulin, UB roll, jelly roll, plaitfold (Fig.1and Fig. 2) (Salem, 1999). One possible factor generating the non-uniform distribution of proteins among folds is the physico-chemical properties that determine topological constraints shaping the realized morphospace of proteins (Anfinsen, 1973; Levitt et al., 1997). Therefore, proteins provide us with a good model for studying patterns in phenotype space and processes underlying the generation of morphotypes.
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