Derivation of the small-angle x-ray scattering functions for local conformations of polypeptide chains in solution

The small-angle x-ray scattering (SAXS) functions are analytically derived for both the randomly coiled and helical local conformations of a polypeptide chain in solution. The resulting scattering functions for helices of carious ty pes are characterized by a maximum in the range of scattering-rector corresponding to Bragg spacings of 3-5 Angstrom, whereas the random-coil function has no maximum. This result is compatible with the extant SAXS data for partially neutralized poly(L-glutamic acid) and poly(L-lysine) in aqueous solutions. Comparison of the SAXS data for the calculated scattering functions shows that helical structures in both polypeptide chains are of the 3.6(13)-helix (alpha -helix) rather than 3.0(10)-type. (C) 2001 John Wiley & Sons, Inc.