The Structure of a Full-length Response Regulator from Mycobacterium tuberculosis in a Stabilized Three-dimensional Domain-swapped, Activated State

Jack King-Scott,Elzbieta Nowak,Efstratios Mylonas,Santosh Panjikar,Manfred Roessle,Dmitri I Svergun,Paul A Tucker

doi:10.1074/jbc.m705081200

Abstract

The full-length, two-domain response regulator RegX3 from Mycobacterium tuberculosis is a dimer stabilized by three-dimensional domain swapping. Dimerization is known to occur in the OmpR/PhoB subfamily of response regulators upon activation but has previously only been structurally characterized for isolated receiver domains. The RegX3 dimer has a bipartite intermolecular interface, which buries 2357 A(2) per monomer. The two parts of the interface are between the two receiver domains (dimerization interface) and between a composite receiver domain and the effector domain of the second molecule (interdomain interface). The structure provides support for the importance of threonine and tyrosine residues in the signal transduction mechanism. These residues occur in an active-like conformation stabilized by lanthanum ions. In solution, RegX3 exists as both a monomer and a dimer in a concentration-dependent equilibrium. The dimer in solution differs from the active form observed in the crystal, resembling instead the model of the inactive full-length response regulator PhoB.

Highlights

Some two-component system (TCS) appear to be essential for the survival of bacteria, and to date homologous TCS have not been identified in the animal kingdom
M. tuberculosis contains 30 genes encoding TCS proteins [6], 12 complete TCS, and several orphan TCS proteins possibly belonging to the sensor histidine kinase (SK) and RR families [6, 7]
The production of M. tuberculosis strains with a compromised senX3-regX3 operon has shown that an intact SenX3-RegX3 TCS is required for a progressive infection [10]

Summary

Introduction

The predominant signaling system for adaptive gene expression changes in bacteria is called a two-component system (TCS). TCS are found in eubacteria, archaea, and eukarya; Some TCS appear to be essential for the survival of bacteria, and to date homologous TCS have not been identified in the animal kingdom. Dimerization has been suggested as important for signal transduction in other OmpR/PhoB members This is based upon several biochemical experiments and the two full-length crystal structures of DrrD [22] and DrrB [23], which are both open structures with accessible recognition helices. The ␣4-␤5-␣5 face of the receiver domain of a RR is the region most affected by phosphorylation and is the proposed site of dimerization in the OmpR/PhoB family. This site in this family displays high residue conservation as compared with other RR families [4], consistent with the importance of this region as a dimerization interface. We present an analysis of the solution structure of RegX3 in an inactive form as both a monomer and dimer

Results

Discussion

Conclusion