Halo-Archaeal Thioredoxin: A Novel Solubility-Enhancing Partner Protein for Fusion Protein Expression

Abstract

A gene for halophilic thioredoxin （TrxA） was isolated from extreme halophile, Halobacterium sp. NRC-1. The TrxA was highly soluble with or without high salt concentrations. Circular dichroism and thiol-disulfide oxidoreductase activity demonstrated that TrxA unfolded at low salt concentrations, and folded and was active at high salt concentrations. Folding/unfolding of TrxA was clearly salt dependent, and highly reversible. This halophilic TrxA was employed to develop a solubility-enhancing partner protein for the expression of fusion proteins. TrxA-amylase fusion protein was expressed in Escherichia coli in soluble form with a～ 2.5-fold higher amount than the β-lactamase-amylase fusion protein previously reported.