Summary: Raman Studies of Solution Polyglycine Conformations
Sergei Bykov and Sanford Asher*
Department of Chemistry, UniVersity of Pittsburgh, Pittsburgh, PennsylVania 15260
ReceiVed: January 4, 2010; ReVised Manuscript ReceiVed: March 6, 2010
Polyglycine (polygly) is an important model system for understanding the structural preferences of unfolded
polypeptides in solution. We utilized UV resonance and visible Raman spectroscopy to investigate the
conformational preferences of polygly peptides of different lengths in water containing LiCl and LiClO4.
Lithium salts increase the solubility of polygly. Our study indicates that in solution the conformational ensemble
of polygly, as well as central peptide bonds of gly5 and gly6, are dominated by the 31 extended helix, also
known as the polyglycine II conformation (PGII). This preference of the polygly backbone for the PGII
conformation in solution is likely a result of favorable interactions between carbonyl dipoles in these extended
helices. We found that high concentrations of Li+
stabilize the PGII conformation in solution, most likely by
polarizing the peptide bond carbonyls that makes PGII-stabilizing carbonyl-carbonyl electrostatic interactions
more favorable. This ability of Li+
to stabilize 31-helix conformations in solution gives use to the denaturing
ability of lithium salts.
Polyglycine (polygly) occurs in two major structural forms
in the solid state, polyglycine I (PGI) and polyglycine II (PGII).