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10th International Congress "Cell Volume Regulation: Novel Therapeutic Targets and Pharmacological Approaches"
THE ROLE OF THE MSCS CYTOPLASMIC VESTIBULUM
IN THE CHANNEL ION SELECTIVITY AND REGULATION OF INTRACELLULAR CALCIUM
Cox, C.D.1, Nomura, T.2, Ziegler, C.S.3, Campbell, A.K.1, Wann, K.T.1, and Martinac, B.1' 4
1 School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Cardiff UK
2 Victor Chang Cardiac Research Institute, Sydney, Australia
3 Department of Pharmacy, Centre for Drug Research, Ludwig-Maximilians- Universität München, Munich, Germany
4 St. Vincent's Clinical School, University of New South Wales, Kensington, Australia
The mechanosensitive (MS) channel of small conductance (MscS) has been characterized at both functional and structural levels and plays an integral role in protection of bacterial cells against hypoosmotic shock. In this study we investigated the role that the cytoplasmic domain plays in MscS channel function by investigating ion selectivity and gating properties in solutions containing different mono- and divalent cations. Our results show that MscS preferentially resides in subconducting states at hy-perpolarising potentials when Ca2+ and Ba2+ ions are the major permeant cations. In addition, our results indicate that charged residues proximal to the seven vestibular portals and their electrostatic interactions with permeating cations determine selectivity and regulate conductance of MscS and potentially other channels belonging to the MscS subfamily. We compared the selectivity of several members of the MscS-like channel subfamily, whose ion conducting properties were previously investigated and reported, using them as natural variations of the vestibular
primary structure reflected by their ion selectivity. Furthermore, we also mutagenized two carefully chosen charged residues within the cytoplasmic chamber of MscS of E. coli. Our choice was based on detailed analysis of the possible effects of different mutations on the electronegative area within the vestibulum of MscS. Together these data provide strong evidence for the role of the C-terminal domain as a selectivity filter in MscS-like channels. Most interestingly of all that on opening MS channels can become not only a passageway for osmolyte exit but also a conduit for the entry of ions including Ca2+ suggesting a role for the MS channels in bacterial calcium regulation indicative of functions other than protection against osmolarity changes. In conclusion, our results have important implications for the physiology of bacterial cells. Supported by the School of Pharmacy and Pharmaceutical Sciences and Cardiff University Endowment Fund (C. D. C.) and National Medical and Health Research Council of Australia (B. M.).
Бюллетень сибирской медицины, 2013, том 12, № 4, с. 24-68
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