open access

https://hdl.handle.net/2115/78774

Interhelical interactions between D92 and C218 in the cytoplasmic domain regulate proton uptake upon N-decay in the proton transport of Acetabularia rhodopsin II

英語

Switching

2018-06

Elsevier

Journal of photochemistry and photobiology B-biology

183

35-45

Acetabularia rhodopsin II (ARII or Ace2), an outward light-driven algal proton pump found in the giant unicellular marine alga Acetabularia acetabulum, has a unique property in the cytoplasmic (CP) side of its channel. The X-ray crystal structure of ARII in a dark state suggested the formation of an interhelical hydrogen bond between C218(ARII) and D92(ARII), an internal proton donor to the Schiff base (Wada et al., 2011). In this report, we investigated the photocycles of two mutants at position C218(ARII): C218(AAII) which disrupts the interaction with D92(ARII), and C218S(ARII) which potentially forms a stronger hydrogen bond. Both mutants exhibited slower photocycles compared to the wild-type pump. Together with several kinetic changes of the photoproducts in the first half of the photocycle, these replacements led to specific retardation of the N-to-O transition in the second half of the photocycle. In addition, measurements of the flash-induced proton uptake and release using a pH sensitive indium-tin oxide electrode revealed a concomitant delay in the proton uptake. These observations strongly suggest the importance of a native weak hydrogen bond between C218(ARII) and D92(ARII) for proper proton translocation in the CP channel during N-decay. A putative role for the D92(ARII)-C218(ARII) interhelical hydrogen bond in the function of ARII is discussed.

学術雑誌論文

Accepted Manuscript

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1011-1344