Mechanism of formation of the C‐terminal β‐hairpin of the B3 domain of the immunoglobulin‐binding protein G from Streptococcus. IV. Implication for the mechanism of folding of the parent protein

Abstract

A 34‐residue α/β peptide [IG(28–61)], derived from the C‐terminal part of the B3 domain of the immunoglobulin binding protein G from Streptoccocus, was studied using CD and NMR spectroscopy at various temperatures and by differential scanning calorimetry. It was found that the C‐terminal part (a 16‐residue‐long fragment) of this peptide, which corresponds to the sequence of the β‐hairpin in the native structure, forms structure similar to the β‐hairpin only at T = 313 K, and the structure is stabilized by non‐native long‐range hydrophobic interactions (Val47–Val59). On the other hand, the N‐terminal part of IG(28–61), which corresponds to the middle α‐helix in the native structure, is unstructured at low temperature (283 K) and forms an α‐helix‐like structure at 305 K, and only one helical turn is observed at 313 K. At all temperatures at which NMR experiments were performed (283, 305, and 313 K), we do not observe any long‐range connectivities which would have supported packing between the C‐terminal (β‐hairpin) and the N‐terminal (α‐helix) parts of the sequence. Such interactions are absent, in contrast to the folding pathway of the B domain of protein G, proposed recently by Kmiecik and Kolinski (Biophys J 2008, 94, 726–736), based on Monte‐Carlo dynamics studies. Alternative folding mechanisms are proposed and discussed. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 469–480, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com