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Differential backbone dynamics of companion helices in the extended helical coiled-coil domain of a bacterial chemoreceptor.

ABSTRACT: Cytoplasmic domains of transmembrane bacterial chemoreceptors are largely extended four-helix coiled coils. Previous observations suggested the domain was structurally dynamic. We probed directly backbone dynamics of this domain of the transmembrane chemoreceptor Tar from Escherichia coli using site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy. Spin labels were positioned on solvent-exposed helical faces because EPR spectra for such positions reflect primarily polypeptide backbone movements. We acquired spectra for spin-labeled, intact receptor homodimers solubilized in detergent or inserted into native E. coli lipid bilayers in Nanodiscs, characterizing 16 positions distributed throughout the cytoplasmic domain and on both helices of its helical hairpins, one amino terminal to the membrane-distal tight turn (N-helix), and the other carboxyl terminal (C-helix). Detergent solubilization increased backbone dynamics for much of the domain, suggesting that loss of receptor activities upon solubilization reflects wide-spread destabilization. For receptors in either condition, we observed an unanticipated difference between the N- and C-helices. For bilayer-inserted receptors, EPR spectra from sites in the membrane-distal protein-interaction region and throughout the C-helix were typical of well-structured helices. In contrast, for approximately two-thirds of the N-helix, from its origin as the AS-2 helix of the membrane-proximal HAMP domain to the beginning of the membrane-distal protein-interaction region, spectra had a significantly mobile component, estimated by spectral deconvolution to average approximately 15%. Differential helical dynamics suggests a four-helix bundle organization with a pair of core scaffold helices and two more dynamic partner helices. This newly observed feature of chemoreceptor structure could be involved in receptor function.

SUBMITTER: Bartelli NL

PROVIDER: S-EPMC4622210 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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Differential backbone dynamics of companion helices in the extended helical coiled-coil domain of a bacterial chemoreceptor.

Bartelli Nicholas L NL Hazelbauer Gerald L GL

Protein science : a publication of the Protein Society 20150825 11

Cytoplasmic domains of transmembrane bacterial chemoreceptors are largely extended four-helix coiled coils. Previous observations suggested the domain was structurally dynamic. We probed directly backbone dynamics of this domain of the transmembrane chemoreceptor Tar from Escherichia coli using site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy. Spin labels were positioned on solvent-exposed helical faces because EPR spectra for such positions reflect primarily po ...[more]

PMID: 26257396

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Dataset Information

Differential backbone dynamics of companion helices in the extended helical coiled-coil domain of a bacterial chemoreceptor.

Publications

Differential backbone dynamics of companion helices in the extended helical coiled-coil domain of a bacterial chemoreceptor.

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