Thermal and chemical unfolding studies in chemotaxis heme sensors from Geobacter sulfurreducens

摘要

The thermal and chemical unfolding mechanisms of periplasmic hemic sensor domains GSU0582 and GSU0935 were investigated by far-UV CD and UV-visible spectra. The sensors have a reversible two-state cooperative unfolding mechanism, with different Tm, Cm and conformation stability parameters, suggesting that GSU0582 is conformationally more stable. These findings and differences in the dynamic properties of the two sensors might provide clues into dimer assembly.Sensing and responding to extracellular conditions in a timely manner is essential for bacterial survival. Geobacter sulfurreducens (Gs) is an anaerobic bacterium that displays a considerable respiratory versatility. The Gs genome encodes for an unusual family of ten heme sensor proteins, each containing at least one heme c-binding motif1. Sensors GSU0582 and GSU0935 (hereafter 582 and 935), are methyl-accepting chemotaxis proteins and have similar predicted topologies: an N-terminal tail in the cytoplasm, followed by a transmembrane helix, a periplasmic domain (about 135 residues), another transmembrane helix, and transducer cytoplasmic domains. The heme sensor domains form swapped dimers and have a PAS-type fold1. As a first step towards rationalization of dimerization mechanism, we addressed the unfolding properties of these two sensor domains.