Article

Salt-driven equilibrium between two conformations in the HAMP domain from Natronomonas pharaonis: the language of signal transfer?

Fachbereich Physik, Universität Osnabrück, Barbarastrasse 7, 49076 Osnabrück, Germany.
Journal of Biological Chemistry (Impact Factor: 4.6). 09/2008; 283(42):28691-701. DOI: 10.1074/jbc.M801931200
Source: PubMed

ABSTRACT HAMP domains (conserved in histidine kinases, adenylyl cyclases, methyl-accepting chemotaxis proteins, and phosphatases) perform their putative function as signal transducing units in diversified environments in a variety of protein families. Here the conformational changes induced by environmental agents, namely salt and temperature, on the structure and function of a HAMP domain of the phototransducer from Natronomonas pharaonis (NpHtrII) in complex with sensory rhodopsin II (NpSRII) were investigated by site-directed spin labeling electron paramagnetic resonance. A series of spin labeled mutants were engineered in NpHtrII157, a truncated analog containing only the first HAMP domain following the transmembrane helix 2. This truncated transducer is shown to be a valid model system for a signal transduction domain anchored to the transmembrane light sensor NpSRII. The HAMP domain is found to be engaged in a "two-state" equilibrium between a highly dynamic (dHAMP) and a more compact (cHAMP) conformation. The structural properties of the cHAMP as proven by mobility, accessibility, and intra-transducer-dimer distance data are in agreement with the four helical bundle NMR model of the HAMP domain from Archaeoglobus fulgidus.

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