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: 4.57). 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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    • "A more detailed SDSL EPR study on the first NpHtrII HAMP domain investigating the structural and dynamic features in dependency of salt concentration (Figure 4B) and temperature revealed that the HAMP domain is engaged in a " two-state " equilibrium between a highly dynamic (dHAMP) and a compact (cHAMP) conformation (Döbber et al., 2008) (Figure 5). The structural properties of the cHAMP conformation as proven by mobility, accessibility, and intra-transducer-dimer distance data were found to be in agreement with the four helical bundle NMR model of the HAMP domain from Archaeoglobus fulgidus. "
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    ABSTRACT: Archaeal photoreceptors, together with their cognate transducer proteins, mediate phototaxis by regulating cell motility through two-component signal transduction pathways. This sensory pathway is closely related to the bacterial chemotactic system, which has been studied in detail during the past 40 years. Structural and functional studies applying site-directed spin labelling and electron paramagnetic resonance spectroscopy on the sensory rhodopsin II/transducer (NpSRII/NpHtrII) complex of Natronomonas pharaonis have yielded insights into the structure, the mechanisms of signal perception, the signal transduction across the membrane and provided information about the subsequent information transfer within the transducer protein towards the components of the intracellular signalling pathway. Here, we provide an overview about the findings of the last decade, which, combined with the wealth of data from research on the Escherichia coli chemotaxis system, served to understand the basic principles microorganisms use to adapt to their environment. We document the time course of a signal being perceived at the membrane, transferred across the membrane and, for the first time, how this signal modulates the dynamic properties of a HAMP domain, a ubiquitous signal transduction module found in various protein classes.
    European journal of cell biology 06/2011; 90(9):731-9. DOI:10.1016/j.ejcb.2011.04.013 · 3.70 Impact Factor
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    • "HAMP domains are highly dynamic (Doebber et al., 2008), and the rapid degree of crosslinking suggests that structural oscillations bring the AS2 helices, but not the AS1 helices, into close proximity, as observed in the HAMP2 conformation. EPR studies of NpHtrII found that the HAMP domain oscillates between two conformations: one resembling the compact Af1503 structure and another corresponding to a more-expanded, solvent exposed conformation (Doebber et al., 2008). The most dynamic region of NpHtrII was the C-terminal region of AS1, an observation consistent with the separation of AS1 from the bundle in the highly trapezoidal structure of HAMP2. "
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    ABSTRACT: HAMP domains are widespread prokaryotic signaling modules found as single domains or poly-HAMP chains in both transmembrane and soluble proteins. The crystal structure of a three-unit poly-HAMP chain from the Pseudomonas aeruginosa soluble receptor Aer2 defines a universal parallel four-helix bundle architecture for diverse HAMP domains. Two contiguous domains integrate to form a concatenated di-HAMP structure. The three HAMP domains display two distinct conformations that differ by changes in helical register, crossing angle, and rotation. These conformations are stabilized by different subsets of conserved residues. Known signals delivered to HAMP would be expected to switch the relative stability of the two conformations and the position of a coiled-coil phase stutter at the junction with downstream helices. We propose that the two conformations represent opposing HAMP signaling states and suggest a signaling mechanism whereby HAMP domains interconvert between the two states, which alternate down a poly-HAMP chain.
    Structure 03/2010; 18(4):436-48. DOI:10.1016/j.str.2010.01.013 · 6.79 Impact Factor
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    • "The bundle stability model may also apply to the HAMP domains of signaling proteins other than chemoreceptors. There is evidence for a dynamic or unstructured HAMP state in several other systems (Bordignon et al., 2005; Kishii et al., 2007; Doebber et al., 2008) and the paucity of high-resolution structures implies that HAMP domains could be highly dynamic under physiological conditions. Indeed, the Af1503 HAMP bundle may have been unusually stable because it was examined well below its normal operating temperature (Hulko et al., 2006). "
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    ABSTRACT: To test the gearbox model of HAMP signalling in the Escherichia coli serine receptor, Tsr, we generated a series of amino acid replacements at each residue of the AS1 and AS2 helices. The residues most critical for Tsr function defined hydrophobic packing faces consistent with a four-helix bundle. Suppression patterns of helix lesions conformed to the predicted packing layers in the bundle. Although the properties and patterns of most AS1 and AS2 lesions were consistent with both proposed gearbox structures, some mutational features specifically indicate the functional importance of an x-da bundle over an alternative a-d bundle. These genetic data suggest that HAMP signalling could simply involve changes in the stability of its x-da bundle. We propose that Tsr HAMP controls output signals by modulating destabilizing phase clashes between the AS2 helices and the adjoining kinase control helices. Our model further proposes that chemoeffectors regulate HAMP bundle stability through a control cable connection between the transmembrane segments and AS1 helices. Attractant stimuli, which cause inward piston displacements in chemoreceptors, should reduce cable tension, thereby stabilizing the HAMP bundle. This study shows how transmembrane signalling and HAMP input-output control could occur without the helix rotations central to the gearbox model.
    Molecular Microbiology 08/2009; 73(5):801-14. DOI:10.1111/j.1365-2958.2009.06819.x · 5.03 Impact Factor
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