Fold patterns limited number

With the realization that there are only a limited number of stable folds and many unrelated sequences that have the same fold, biologically oriented computer scientists started to address what is called the inverse folding problem namely, which sequence patterns are compatible with a specific fold If this question can be answered, such patterns could be used to search through the genome sequence databases and extract those sequences that have a specific fold, such as the cx/p barrel or the immunoglobulin fold. 

The ligand binding or catalytic sites are the most relevant parts of a protein domain for the development of small molecules as modulators of protein function. There is evidence that proteins with conserved folds often also have their functional sites on the same topological location. In some cases a remarkable conservatism in functional sites can be observed. This is true for the example described later in this review on similarity of Cdc25A phosphatase, acetylcholinesterase (AChE) and 1 Ifl-hydroxysteroid dehydrogenases (1 l HSD) (Fig. 9). Nevertheless, it should be stressed that the correlation patterns of amino acid sequence, protein fold and protein function remain a matter of debate. Moreover, a vast number of specific functions can be carried out by the limited number of protein domains due to the high amino acid diversity of proteins with similar folds. " ... 

Polypeptide chains fold in a limited number of well-defined structural patterns,... 

A number of investigators have performed drawing and annealing experiments on acrylic polymers, copolymers, and fibers that provide support for a limited two-phase model of the structure [143,149-153]. Hinrichsen and Orth [149], for example, have observed periodicities on the order of 120-105 A in the small-angle x-ray pattern of drawn films of the PAN homopolymer. These observations strongly suggest the presence of a two-phase structure, perhaps with lamellar crystalline units, separated by less-ordered material of the chain-folded lamellae [154]. Hinrichsen [143] has observed a similar behavior in drawn PAN fibers. 

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