STATIC AND DYNAMIC PROPERTIES OF A NEW LATTICE MODEL OF POLYPEPTIDE-CHAINS

The equilibrium and dynamic properties of a new lattice model of proteins are explored in the athermal limit. In this model, consecutive alpha-carbons of the model polypeptide are connected by vectors of the type (+/- 2, +/- 1,0). In all cases, the chains have a finite backbone thickness which is close to that present in real proteins. Three different polypeptides are examined: polyglycine, polyalanine, and polyleucine. In the latter two cases, the side chains (whose conformations are extracted from known protein crystal structures) are included. For the equilibrium chain dimensions, with increasing side chain bulkiness, the effective chain length is smaller. The calculations suggest that these model polypeptides are in the same universality class as other polymer models. One surprising result is that although polyalanine and polyleucine have chiral sidechains, they do not induce a corresponding handedness of the main chain. For both polyleucine and polyalanine, the scaling of the self-diffusion constant and the terminal relaxation time are consistent with Rouse dynamics of excluded volume chains. Polyglycine exhibits a slightly stronger chain length dependence for these properties. This results from a finite length effect due to moderately long lived, local self-entanglements arising from the thin effective cross section of the chain backbone.