Glycine betaine-assisted protein folding in a lysA mutant of Escherichia coli

Osmoprotectants exogenously supplied to a hyperosmotic culture medium are e fficiently imported and amassed by stressed cells of Escherichia coil, In a ddition to their evident role in the recovery and maintenance of osmotic ba lance, these solutes should play an important role on the behavior of cellu lar macromolecules, for example in the process of protein folding, Using a random chemical mutagenesis approach, a conditional lysine auxotrophic muta nt was obtained. The growth of this mutant was restored by addition of eith er lysine or osmoprotectants including glycine betaine (GB) in the minimal medium. The growth rate increased proportionally with the augmentation of t he intracellular GB concentration. The mutation was located in the lysA gen e and resulted in the substitution of the Ser at position 384 by Phe of the diaminopimelate decarboxylase (DAPDC), which catalyzes the conversion of m eso-diaminopimelate to L-lysine. We purified both the wild type DAPDC and t he mutated DAPDC-sf and demonstrated that GB was capable of activating DAPD C-sf in vitro, thus confirming the in vivo results. Most importantly, we sh owed that the activation was correlated with a conformational change of DAP DC-sf. Taken together, these results show, for the first time, that GB may actively assist in vivo protein folding in a chaperone-like manner.