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J. Biol. Chem., Vol. 283, Issue 42, 28691-28701, October 17, 2008

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Salt-driven Equilibrium between Two Conformations in the HAMP Domain from Natronomonas pharaonis

THE LANGUAGE OF SIGNAL TRANSFER?^*

Meike Doebber, Enrica Bordignon¹, Johann P. Klare, Julia Holterhues, Swetlana Martell, Nadine Mennes, Lin Li, Martin Engelhard², and Heinz-Jürgen Steinhoff³

From the Fachbereich Physik, Universität Osnabrück, Barbarastrasse 7, 49076 Osnabrück, Germany and the Max-Planck-Institut für Molekulare Physiologie, Otto-Hahn-Str. 11, 44227 Dortmund, Germany

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.

Received for publication, March 10, 2008 , and in revised form, August 6, 2008.

^* This work was supported by Deutsche Forschungsgemeinschaft Grants SFB 431/P18 (to J. P. K. and H. J. S.) and EN87/14-2 (to M. E.) and the Max Planck Society (to M. E.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Present address: Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.

² To whom correspondence may be addressed. Tel.: 49-231-1332302; Fax: 49-231-1332399; E-mail: martin.engelhard{at}mpi-dortmund.mpg.de.

³ To whom correspondence may be addressed. Tel.: 49-541-9692675; Fax: 49-541-9692656; E-mail: hsteinho{at}uos.de.

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