Hydrogen Bonding Alteration of Thr-204 in the Complex between pharaonis Phoborhodopsin and Its Transducer Protein

Yuki Sudo, Yuji Furutani, Kazumi Shimono, Naoki Kamo, Hideki Kandori


45 被引用数 (Scopus)


pharaonis phoborhodopsin (ppR, also called pharaonis sensory rhodopsin II, psRII) is a receptor for negative phototaxis in Natronobacterium pharaonis. It forms a 2:2 complex with its transducer protein, pHtrII, in membranes and transmits light signals through the change in the protein-protein interaction. We previously found that the ppRK minus ppR spectrum in D20 possesses vibrational bands of ppR at 3479 (-)/3369 (+) cm-1 only in the presence of pHtrII [Furutani, Y., Sudo, Y., Kamo, N., and Kandori, H. (2003) Biochemistry 42, 4837-4842]. A D/H-unexchangeable X-H group appears to form a stronger hydrogen bond upon retinal photoisomerization in the ppR-pHtrII complex. This article aims to identify the group by use of various mutant proteins. According to the crystal structure, Tyr-199 of ppR forms a hydrogen bond with Asn-74 of pHtrII in the complex. Nevertheless, the 3479 (-)/3369 (+) cm-1 bands were preserved in the Y199F mutant, excluding the possibility that the bands are O-H stretches of Tyr-199. On the other hand, Thr-204 and Tyr-174 form a hydrogen bond between the retinal chromophore pocket and the binding surface of the ppR-pHtrII complex. These FTIR measurements revealed that the bands at 3479 (-)/3369 (+) cm-1 disappeared in the T204A mutant, while being shifted to 3498 (-) and 3474 (+) cm-1 in the T204S mutant. They appear at 3430 (-)/3402 (+) cm-1 in the Y174F mutant. From these results, we concluded that the bands at 3479 (-)/3369 (+) cm-1 originate from the O-H stretch of Thr-204. A stronger hydrogen bond as shown by a large spectral downshift (110 cm-1) suggests that the specific hydrogen bonding alteration of Thr-204 takes place upon retinal photoisomerization, which does not occur in the absence of the transducer protein. Thr-204 has been known as an important residue for color tuning and photocycle kinetics in ppR. The results presented here point to an additional important role of Thr-204 in ppR for the interaction with pHtrII. Specific interaction in the complex that involves Thr-204 presumably affects the decay kinetics and binding affinity in the M intermediate.

出版ステータスPublished - 12月 9 2003

ASJC Scopus subject areas

  • 生化学


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