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Functional importance of the oligomer formation of the cyanobacterial H(+) pump Gloeobacter rhodopsin

Many microbial rhodopsins self-oligomerize, but the functional consequences of oligomerization have not been well clarified. We examined the effects of oligomerization of a H(+) pump, Gloeobacter rhodopsin (GR), by using nanodisc containing trimeric and monomeric GR. The monomerization did not appea...

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Detalles Bibliográficos
Autores principales: Iizuka, Azusa, Kajimoto, Kousuke, Fujisawa, Tomotsumi, Tsukamoto, Takashi, Aizawa, Tomoyasu, Kamo, Naoki, Jung, Kwang-Hwan, Unno, Masashi, Demura, Makoto, Kikukawa, Takashi
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Nature Publishing Group UK 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6656774/
https://www.ncbi.nlm.nih.gov/pubmed/31341208
http://dx.doi.org/10.1038/s41598-019-47178-5
Descripción
Sumario:Many microbial rhodopsins self-oligomerize, but the functional consequences of oligomerization have not been well clarified. We examined the effects of oligomerization of a H(+) pump, Gloeobacter rhodopsin (GR), by using nanodisc containing trimeric and monomeric GR. The monomerization did not appear to affect the unphotolyzed GR. However, we found a significant impact on the photoreaction: The monomeric GR showed faint M intermediate formation and negligible H(+) transfer reactions. These changes reflected the elevated pKa of the Asp121 residue, whose deprotonation is a prerequisite for the functional photoreaction. Here, we focused on His87, which is a neighboring residue of Asp121 and conserved among eubacterial H(+) pumps but replaced by Met in an archaeal H(+) pump. We found that the H87M mutation removes the “monomerization effects”: Even in the monomeric state, H87M contained the deprotonated Asp121 and showed both M formation and distinct H(+) transfer reactions. Thus, for wild-type GR, monomerization probably strengthens the Asp121-His87 interaction and thereby elevates the pKa of Asp121 residue. This strong interaction might occur due to the loosened protein structure and/or the disruption of the interprotomer interaction of His87. Thus, the trimeric assembly of GR enables light-induced H(+) transfer reactions through adjusting the positions of key residues.