Dynamics and activation in response regulators: the β4-α4 loop.
Two-component signal transduction systems of microbes are a primary means to respond to signals emanating from environmental and metabolic fluctuations as well as to signals coordinating the cell cycle with macromolecular syntheses, among a large variety of other essential roles. Signals are recognized by a sensor domain of a histidine kinase which serves to convert signal binding to an active transmissible phosphoryl group through a signal-induced ATP-dependent autophosphorylation reaction directed to histidine residue. The sensor kinase is specifically mated to a response regulator, to which it transfers the phosphoryl group that activates the response regulator's function, most commonly gene repression or activation but also interaction with other regulatory proteins. Two-component systems have been genetically amplified to control a wide variety of cellular processes; for example, bothEscherichia coliandPseudomonas aeruginosahave 60 plus confirmed and putative two-component systems.Bacillus subtilishas 30 plus andNostoc punctiformisover 100. As genetic amplification does not result in changes in the basic structural folds of the catalytic domains of the sensor kinase or response regulators, each sensor kinase must recognize its partner through subtle changes in residues at the interaction surface between the two proteins. Additionally, the response regulator must prepare itself for efficient activation by the phosphorylation event. In this short review, we discuss the contributions of the critical β4-α4 recognition loop in response regulators to their function. In particular, we focus on this region's microsecond-millisecond timescale dynamics propensities and discuss how these motions play a major role in response regulator recognition and activation.
Department of Molecular and Structural Biochemistry, North Carolina State University, 128 Polk Hall, Raleigh, NC 27695, USA.
Benjamin G
BG
Bobay
Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 N. Torrey Pines Rd., La Jolla, CA 92037, USA.
James A
JA
Hoch
Department of Molecular and Structural Biochemistry, North Carolina State University, 128 Polk Hall, Raleigh, NC 27695, USA.
John
J
Cavanagh
NMR; millisecond dynamics; phosphorylation; response regulator; β4-α4 recognition loop