Carboxyl pK(a) values, ion pairs, hydrogen bonding, and the pH-dependence of folding the hyperthermophile proteins Sac7d and Sso7d.

ABSTRACT: Sac7d and Sso7d are homologous, hyperthermophile proteins with a high density of charged surface residues and potential ion pairs. To determine the relative importance of specific amino acid side-chains in defining the stability and function of these Archaeal chromatin proteins, pK(a) values were measured for the acidic residues in both proteins using (13)C NMR chemical shifts. The stability of Sso7d enabled titrations to pH 1 under low-salt conditions. Two aspartate residues in Sso7d (D16 and D35) and a single glutamate residue (G54) showed significantly perturbed pK(a) values in low salt, indicating that the observed pH-dependence of stability was primarily due to these three residues. The pH-dependence of backbone amide NMR resonances demonstrated that perturbation of all three pK(a) va

SUBMITTER: Clark AT 

PROVIDER: S-EPMC2083566 | biostudies-literature | 2007 Sep

REPOSITORIES: biostudies-literature