1-Anilino-8-Naphthalene Sulfonate Anion-Protein Binding Depends Primarily on Ion Pair Formation

Abstract

The ANS- (1-anilino-8-naphthalene sulfonate) anion is strongly, dominantly bound to cationic groups of water-soluble proteins and polyamino acids through ion pair formation. This mode of ANS- binding, broad and pH dependent, is expressed by the quite rigorous stoichiometry of ANS- bound with respect to the available summed number of H+ titrated lysine, histidine, and arginine groups. By titration calorimetry, the integral or overall enthalpies of ANS- binding to four proteins, bovine serum albumin, lysozyme, papain, and protease omega, were arithmetic sums of individual ANS(-)-polyamino acid sidechain binding enthalpies (polyhistidine, polyarginine, polylysine), weighted by numbers of such cationic groups of each protein (additivity of binding enthalpies). ANS- binding energetics to both classes of macromolecules, cationic proteins and synthetic cationic polyamino acids, is reinforced by the organic moiety (anilinonaphthalene) of ANS-. In a much narrower range of binding, where ANS- is sometimes assumed to act as a hydrophobic probe, ANS- may become fluorescent. However, the broad overall range is sharply dependent on electrostatic, ion pair formation, where the organic sulfonate group is the major determinant of binding.

The protective effect of crocin on the amyloid fibril formation of aβ42 peptide in vitro

“…2A and B and Table 1, it is reasonable to conclude that after incubation with crocin, Aβ 42 develops a partial helical structure. The evaluation of the CD peak supports the idea that crocin causes Aβ 42 to form an alpha-helix structure that is a non-amyloidogenic conformer [25]. Possible reasons for this observation are provided below.…”

“…ANS is a hydrophobic fluorescent molecular probe that has been used for examining the non-polar character of proteins and membranes [23][24][25]. ANS binding is used to study changes in exposed hydrophobicity in Aβ 42 upon incubation in the presence and absence of crocin.…”

Molten globule state of tear lipocalin: ANS binding restores tertiary interactions

“…Fluorescence enhancement upon binding to proteins can result from ion pairing interactions, hydrophobic interactions, restricted mobility or any combination of these factors [33][34][35][36]. EPR spectra of spin labeled G-strand mutants complexed with ANS in molten globule state are shown in Figure 1.…”

Unfolding Studies of Escherichia coli Maltodextrin Glucosidase Monitored by Fluorescence Spectroscopy

“…An ANS-binding study was performed in detail to understand how the surface hydrophobicity of MalZ changes during unfolding process as well as to gain better insight into the mechanism of in vitro unfolding of the protein. ANS (1-anilino-8-naphthalenesulfonate) is a much-utilized fluorescent "hydrophobic probe" for examining the non-polar character of a protein [15]. It is generally assumed that if ANS becomes brilliantly fluorescent upon binding a host protein, the binding sites were nonpolar and hydrophobic during association.…”