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J Photochem Photobiol B. 2018 Jun;183:35-45. doi: 10.1016/j.jphotobiol.2018.04.012. Epub 2018 Apr 11.

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

Author information

1
College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan. Electronic address: jtamoga@g.matsuyama-u.ac.jp.
2
Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan; Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo 001-0021, Japan.
3
College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
4
RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan; RIKEN Center for Life Science Technologies, Yokohama 230-0045, Japan.
5
College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan; Graduate School of Pharmaceutical Sciences, Toho University, Funabashi, Chiba 274-8510, Japan.
6
RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan; RIKEN Structural Biology Laboratory, Yokohama 230-0045, Japan.
7
College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan; Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan.

Abstract

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 C218ARII and D92ARII, an internal proton donor to the Schiff base (Wada et al., 2011). In this report, we investigated the photocycles of two mutants at position C218ARII: C218AARII which disrupts the interaction with D92ARII, and C218SARII 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 C218ARII and D92ARII for proper proton translocation in the CP channel during N-decay. A putative role for the D92ARII-C218ARII interhelical hydrogen bond in the function of ARII is discussed.

KEYWORDS:

Hydrogen bond; Microbial rhodopsin; Photocycle; Proton pump; Switching

[Indexed for MEDLINE]

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