Hydrogen bonding and equilibrium protium-deuterium fractionation factors in the immunoglobulin G binding domain of protein G.

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TitleHydrogen bonding and equilibrium protium-deuterium fractionation factors in the immunoglobulin G binding domain of protein G.
Publication TypeJournal Article
Year of Publication1999
AuthorsKhare, D, Alexander, P, Orban, J
JournalBiochemistry
Volume38
Issue13
Pagination3918-25
Date Published1999 Mar 30
ISSN0006-2960
KeywordsAmino Acid Sequence, Bacterial Proteins, Deuterium, Hydrogen, Hydrogen Bonding, Immunoglobulin G, Models, Molecular, Molecular Sequence Data, Nuclear Magnetic Resonance, Biomolecular, Protein Conformation, Protein Structure, Secondary, Receptors, IgG, Streptococcus
Abstract

Protium-deuterium fractionation factors (phi) were determined for more than 85% of the backbone amide protons in the IgG binding domains of protein G, GB1 and GB2, from NMR spectra recorded over a range of H2O/D2O solvent ratios. Previous studies suggest a correlation between phi and hydrogen bond strength; amide and hydroxyl groups in strong hydrogen bonds accumulate protium (phi < 1), while weak hydrogen bonds accumulate deuterium (phi > 1). Our results show that the alpha-helical residues have slightly lower phi values (1.03 +/- 0.05) than beta-sheet residues (1.12 +/- 0.07), on average. The lowest phi value obtained (0.65) does not involve a backbone amide but rather is for the interaction between two side chains, Y45 and D47. Fractionation factors for solvent-exposed residues are between the alpha-helix and beta-sheet values, on average, and are close to those for random coil peptides. Further, the difference in phiav between alpha-helix and solvent-exposed residues is small, suggesting that differences in hydrogen bond strength for intrachain hydrogen bonds and amide...water hydrogen bonds are also small. Overall, the enrichment for deuterium suggests that most backbone...backbone hydrogen bonds are weak.

DOI10.1021/bi9827114
Alternate JournalBiochemistry
PubMed ID10194303