title: Effective charge measurements reveal selective and preferential accumulation of anions, but not cations, at the protein surface in dilute salt solutions.
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 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)(-) ∼ 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.
authors: Process and Product Development, Amgen Inc. Seattle, Washington 98119, USA. gokarn.yatin@gene.com
authors: Yatin R
authors: YR
authors: Gokarn
authors: R Matthew
authors: RM
authors: Fesinmeyer
authors: Atul
authors: A
authors: Saluja
authors: Vladimir
authors: V
authors: Razinkov
authors: Susan F
authors: SF
authors: Chase
authors: Thomas M
authors: TM
authors: Laue
authors: David N
authors: DN
authors: Brems
mesh_terms: D000818:Animals; D000838:Anions / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D002645:Chickens; D009113:Muramidase / Q000737:chemistry; D012492:Salts / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D000838:Anions; D002412:Cations; D012492:Salts; D012996:Solutions; C421864:hen egg lysozyme; D009113:Muramidase