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Effective charge measurements reveal selective and preferential accumulation of anions, but not cations, at the protein surface in dilute salt solutions
Author(s) -
Gokarn Yatin R.,
Fesinmeyer R.Matthew,
Saluja Atul,
Razinkov Vladimir,
Chase Susan F.,
Laue Thomas M.,
Brems David N.
Publication year - 2011
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.591
Subject(s) - chemistry , lysozyme , salt (chemistry) , hofmeister series , ion , inorganic chemistry , surface charge , crystallography , electrolyte , analytical chemistry (journal) , chromatography , biochemistry , organic chemistry , electrode
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 3 −∼ 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.