1tqg

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(New page: 200px<br /><applet load="1tqg" size="450" color="white" frame="true" align="right" spinBox="true" caption="1tqg, resolution 0.98&Aring;" /> '''CheA phosphotransfer...)
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Revision as of 01:23, 21 November 2007


1tqg, resolution 0.98Å

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CheA phosphotransferase domain from Thermotoga maritima

Overview

Helical histidine phosphotransferase (HPt) domains play a central role in, many aspects of bacterial signal transduction. The 0.98 A resolution, crystallographic structure of the amino-terminal HPt domain (P1) from the, chemotaxis kinase CheA of Thermotoga maritima reveals a remarkable degree, of structural heterogeneity within a four-helix bundle. Two of the four, helices have alternate main-chain conformations that differ by a 1.3-1.7A, shift along the bundle axis. These dual conformers were only resolved with, atomic resolution diffraction data and their inclusion significantly, improved refinement statistics. Neither conformer optimizes packing within, the helical core, consistent with their nearly equal refined occupancies., Altered hydrogen bonding within an inter-helical loop may facilitate, transition between conformers. Two discrete structural states rather than, a continuum of closely related conformations indicates an energetic, barrier to conversion between conformers in the crystal at 100K, although, many more states are expected in solution at physiological temperatures., Anisotropic atomic thermal B factors within the two conformers indicate, modest overall atomic displacement that is largest perpendicular to the, helical bundle and not along the direction of apparent motion. Despite the, conformational heterogeneity of P1 in the crystal at low temperature, the, protein displays high thermal stability in solution (T(m)=100 degrees C)., Addition of a variable C-terminal region that corresponds to a mobile, helix in other CheA structures significantly narrows the temperature width, of the unfolding transition and may affect domain dynamics. Helices that, compose the kinase recognition site and contain the phospho-accepting, His45 do not have alternate conformations. In this region, atomic, resolution provides detailed structural parameters for a conserved, hydrogen-bonding network that tunes the reactivity of His45. A neighboring, glutamate (E67), essential for phosphotransferase activity hydrogen bonds, directly to His45 N(delta1). E67 generates a negative electrostatic, surface surrounding the reactive His that is conserved by most CheA, kinases, but absent in related phosphotransferase proteins. The P1, conformations that we observe are likely relevant to other helical or, coiled-coil proteins and may be important for generating switches in, signaling processes.

About this Structure

1TQG is a Single protein structure of sequence from Thermotoga maritima. Full crystallographic information is available from OCA.

Reference

Helical shifts generate two distinct conformers in the atomic resolution structure of the CheA phosphotransferase domain from Thermotoga maritima., Quezada CM, Gradinaru C, Simon MI, Bilwes AM, Crane BR, J Mol Biol. 2004 Aug 27;341(5):1283-94. PMID:15321722

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