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Cytoplasmic surface structures of bacteriorhodopsin modified by site-directed mutations and cation binding as revealed by 13C NMR

Authors :
Satoru Yamaguchi
Hazime Saitô
Koka Yonebayashi
Satoru Tuzi
Source :
European Biophysics Journal. 32:1-11
Publication Year :
2003
Publisher :
Springer Science and Business Media LLC, 2003.

Abstract

We have examined how cytoplasmic surface structures of [3-(13)C]Ala-labeled bacteriorhodopsin (bR), consisting of the C-terminal alpha-helix and cytoplasmic loops, are altered by site-directed mutations at the former (R227Q) and the latter (A160G, E166G, and A168G) and by cation binding, by means of displacements of the (13)C NMR peaks of Ala228 and Ala233 (C-terminal alpha-helix), Ala103 (C-D loop), and Ala160 (E-F loop). Cytoplasmic ends of the B and F helices were found to undergo fluctuation motions on the order of 10(-5) s, when such surface structures were disrupted, as viewed from suppressed (13)C NMR signals. This happens also for deionized blue membranes of wild type and A160G, with accelerated fluctuations in the loops. Further, cytoplasmic surface structures of Na(+)-regenerated purple membrane from the blue membrane were significantly modified by Ca(2+) ions up to 1 mM under relatively low ionic strength of 10 mM NaCl, although they are very similar at high ionic strength (100 mM NaCl). To interpret these findings, the following two surface structures were proposed. The C-terminal alpha-helix of the wild type at ambient temperature is involved in a perturbed type, probably tilted toward the direction of the B and F helices, to prevent unnecessary fluctuations of these helices for efficient proton uptake during the photocycle. An unperturbed type of helix is achieved when such a surface structure was disrupted at low temperature or in an M-like state. This view is consistent with previously published data for the "proton binding cluster" consisting of Asp104, Glu166, and Glu234.

Details

ISSN :
14321017 and 01757571
Volume :
32
Database :
OpenAIRE
Journal :
European Biophysics Journal
Accession number :
edsair.doi.dedup.....d0e3491ac23a0edb9ec2ded346b2a3b6
Full Text :
https://doi.org/10.1007/s00249-002-0260-0