A highly efficient, one-step purification of the Hsp70 chaperone Ssa1

Abstract

Chaperone proteins are required to maintain the overall fold and function of proteins in the cell. As part of the Hsp70 family, Ssa1 acts to maintain cellular proteostasis through a variety of diverse pathways aimed to preserve the native conformation of target proteins, thereby preventing aggregation and future states of cellular toxicity. Studying the structural dynamics of Ssa1 in vitro is essential to determining their precise mechanisms and requires the development of purification methods that result in highly pure chaperones. Current methods of expressing and purifying Ssa1 utilize affinity tagged constructs expressed in Escherichia coli, however, expression in an exogenous source produces proteins that lack post-translational modifications leading to undesired structural and functional effects. Current protocols to purify Ssa1 from Saccharomyces cerevisiae require large amounts of starting material, multiple steps of chromatography, and result in low yield. Our objective was to establish a small-scale purification of Ssa1 expressed from its endogenous source, Saccharomyces cerevisiae, with significant yield and purity. We utilized a protein A affinity tag that was previously used to purify large protein complexes from yeast, combined with magnetic Dynabeads that are conjugated with rabbit immunoglobulin G (IgG). Our results show that we can produce native, highly pure, active Ssa1 via this one-step purification with minimal amounts of starting material, and this Ssa1-protein A fusion does not alter cellular phenotypes. This methodology is a significant improvement in Ssa1 purification and will facilitate future experiments that will elucidate the biochemical and biophysical properties of Hsp70 chaperones.