The structure and function of the histidine-containing phosphotransfer (HPt) signaling domain of the Escherichia coli ArcB sensor.

The Escherichia coli ArcB sensor is involved in anaerobic signal transduction. ArcB is an unorthodox His-kinase, in that it contains three types of phosphotransfer signaling domains in its primary amino acid sequence, namely, transmitter (or His-kinase), receiver, and histidine-containing phosphotransfer (HPt) domains. In this study, we first conducted an in vivo experiment to determine whether or not the phosphorylation of the HPt domain is crucial for ArcB/ArcA-mediated anaerobic signal transduction. The results are best interpreted as meaning that the HPt domain of ArcB is important for the anaerobic signal transduction, as far as the expression of the succinate dehydrogenase (sdh) operon is concerned. We then isolated a set of ArcB mutant each with a single amino acid substitution in the HPt domain, which has lost the ability to function as a phospho-transmitter. The results of such mutational analyses, together with the three-dimensional crystal structure of the HPt domain, provided an insight into the structure and function of the HPt domain of ArcB.