期刊
PROTEIN SCIENCE
卷 20, 期 3, 页码 580-587出版社
WILEY-BLACKWELL
DOI: 10.1002/pro.591
关键词
ion-protein interactions; protein charge; Hofmeister series; electroselectivity series; specific-ion effects
Specific-ion effects are ubiquitous in nature; however, their underlying mechanisms remain elusive. Although Hofmeister-ion effects on proteins are observed at higher (> 0.3M) salt concentrations, in dilute (< 0.1M) salt solutions nonspecific electrostatic screening is considered to be dominant. Here, using effective charge (Q*) measurements of hen-egg white lysozyme (HEWL) as a direct and differential measure of ion-association, we experimentally show that anions selectively and preferentially accumulate at the protein surface even at low (< 100 mM) salt concentrations. At a given ion normality (50 mN), the HEWL Q* was dependent on anion, but not cation (Li(+), Na(+), K(+), Rb(+), Cs(+), GdnH(+), and Ca(2+)), identity. The Q* decreased in the order F(-) > Cl(-) > Br(-) > NO(3)(-) similar to I(-) > SCN(-) > ClO(4)(-) >> SO(4)(2-), demonstrating progressively greater binding of the monovalent anions to HEWL and also show that the SO(4)(2-) anion, despite being strongly hydrated, interacts directly with the HEWL surface. Under our experimental conditions, we observe a remarkable asymmetry between anions and cations in their interactions with the HEWL surface.
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