NMR solution structure of a cold-adapted thiol-disulfide oxidoreductase

Abstract

Psychrophilic enzymes produced by cold-adapted micro-organisms have successfully overcome the low temperature challenge and adapted to maintain high catalytic rates in their permanently cold environments. The current consensus is that this high activity at low temperatures is mainly achieved through an increase in the flexibility of the protein structure, thereby allowing for the molecular motions necessary for activity in their low thermal energy environment. The actual molecular basis for the adaptation is still however only poorly understood and direct evidence of the proposed increased flexibility is scant, with previous attempts to demonstrate this leading to conflicting results. In an attempt to better understand strategies of cold adaptation we have determined the NMR solution structure of the reduced form of a cold adapted thiol disulphide oxidoreductase (DsbA) isolated from an Antarctic bacterium. While a number of crystal structures for cold adapted enzymes have been published, this is the first report of an NMR structure of these enzymes and thereby opens up a new dimension in the study of cold adaptation. In particular, the potential power of NMR to monitor both local and global motions over a large range of time scales should allow for a better understanding of the role of dynamics in protein adaptation to temperature. The gene encoding the cold-adapted enzyme has been isolated and the protein overexpressed in E. coli with both unlabelled and labelled (15N13C, 15N) protein being purified from the periplasmic extracts. NMR data were acquired on a Bruker AvanceII+ 800 MHz spectrometer and the solution structure of the reduced form of this cold adapted oxidoreductase determined and compared to that of its mesophilic homolog from Vibrio cholerae. In addition, the temperature dependence of activity and stability of both the psychrophile and mesophile have been ascertained and compared. Here, the results of the NMR structure determination and the comparative structural and physicochemical studies of the cold adapted DsbA with its mesophilic homolog will be presented.