Left helix of polyproline II type and genesis of β-structures in spidroins 1 and 2 and their recombinant analogs.

The distribution of secondary structure elements along the polypeptide chains of spider silk proteins spidroins 1 and 2 and their recombinant analogs has been studied by statistical methods. It was found that these proteins as monomers contain only traces of β-structure, while the Ala-rich and the Gly-rich regions are predicted as α-helices and as left-handed helices of polyproline II type. Analysis of literature and our CD data shows that the major polypeptide chain conformation of spidroins 1 and 2 and their recombinant analogs in aqueous solutions is the polyproline II helix, with some α-helices and a very small share of β-structures. The transition to the state with extended conformations, which are characteristic of mature silk fibers, requires dehydration of the polypeptide backbone. Thus, the genesis of β-structure in spider web proteins is determined by the conditions of transitions between the main regular backbone conformations. [ABSTRACT FROM AUTHOR]