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Two Consecutive Polar Amino Acids at the End of Helix E are Important for Fast Turnover of the Archaerhodopsin Photocycle
Author(s) -
Geng Xiong,
Dai Gang,
Chao Luomeng,
Wen Durige,
Kikukawa Takashi,
Iwasa Tatsuo
Publication year - 2019
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.13072
Subject(s) - amino acid , alanine , chemistry , serine , threonine , hydrogen bond , biophysics , stereochemistry , biochemistry , rhodopsin , photochemistry , molecule , biology , enzyme , retinal , organic chemistry
Archaerhodopsins ( AR s) is one of the members of microbial rhodopsins. Threonine 164 (T164) and serine 165 (S165) residues of the AR from Halorubrum sp. ejinoor ( He AR ) are fully conserved in AR s, although they are far from the proton transfer channel and the retinal Schiff base, and are likely involved in a hydrogen‐bonding network at the end of the Helix E where most microbial rhodopsins assume a “bent structure”. In the present work, T164 and/or S165 were replaced with an alanine (A), and the photocycles of the mutants were analyzed with flash photolysis. The amino acid replacements caused profound changes to the photocycle of He AR including prolonged photocycle, accelerated decay of M intermediate and appearance of additional two intermediates which were evident in T164A‐ and T164A/S165A‐ He AR photocyles. These results suggest that although T164 and S165 are located at the far end of the photoactive center, these two amino acid residues are important for maintaining the fast turnover of the He AR photocycle. The underlying molecular mechanisms are discussed in relation to hydrogen‐bonding networks involving these two amino acids. Present study may arouse our interests to explore the functional role of the well‐conserved “bent structure” in different types of microbial rhodopsin.