Effective charge measurements reveal selective and preferential accumulation of anions, but not cations, at the protein surface in dilute salt solutions
✍ Scribed by Yatin R. Gokarn; R.Matthew Fesinmeyer; Atul Saluja; Vladimir Razinkov; Susan F. Chase; Thomas M. Laue; David N. Brems
- Publisher
- Cold Spring Harbor Laboratory Press
- Year
- 2011
- Tongue
- English
- Weight
- 316 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0961-8368
- DOI
- 10.1002/pro.591
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✦ Synopsis
Abstract
Specific‐ion effects are ubiquitous in nature; however, their underlying mechanisms remain elusive. Although Hofmeister‐ion effects on proteins are observed at higher (>0.3__M__) salt concentrations, in dilute (<0.1__M__) 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 m__M__) salt concentrations. At a given ion normality (50 m__N__), 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 ∼ I^−^ > SCN^−^ > ClO ≫ SO, demonstrating progressively greater binding of the monovalent anions to HEWL and also show that the SO 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.