pH dependence of the hydrogen exchange in the SH3 domain of α-spectrin

• Published in: FEBS letters 2002-03, Vol.514 (2), p.295-299
• Main Authors: Sadqi, M., Casares, S., López-Mayorga, O., Martı́nez, J.C., Conejero-Lara, F.
• Format: Article
• Language: English
• Subjects: Amide–hydrogen exchange; Calorimetry; Deuterium - chemistry; HX, hydrogen–deuterium amide exchange; Hydrogen - chemistry; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Models, Molecular; Nuclear magnetic resonance; pH, pH meter reading for deuterium oxide solutions uncorrected from isotopic effects; Protein Conformation; Protein Folding; SH3, Src homology region 3; Spectrin - chemistry; src Homology Domains - physiology; Src homology region 3 domain; Thermodynamics
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(02)02385-2

Using nuclear magnetic resonance we have measured the hydrogen exchange (HX) in the Src homology region 3 (SH3) domain of α-spectrin as a function of pH*. At very acidic pH* values the exchange of most residues appears to occur via global unfolding, although several residues show abnormally large Gibbs energies of exchange, suggesting the presence of some residual structure in the unfolded state. At higher pH* HX occurs mainly via local or partial unfoldings. We have been able to characterize the coupling between the electrostatic interactions in this domain and the conformational fluctuations occurring under native conditions by analyzing the dependence upon pH* of the Gibbs energy of exchange. The SH3 domain seems to be composed of a central core, which requires large structural disruptions to become exposed to the solvent, surrounded by smaller subdomains, which fluctuate independently.