title: Interaction of the protonated Schiff base with the peptide backbone of valine 49 and the intervening water molecule in the N photointermediate of bacteriorhodopsin.
abstract: The effects of replacing Val49, Thr46, Asp96, and Phe219 in the cytoplasmic domain of bacteriorhodopsin on water O-H stretching vibrational bands and the amide I and imide II bands of the peptide backbone were examined in the M, N, and MN intermediates. This study is an extension of previous work on the L photointermediate [Yamazaki, Y., Tuzi, S., Saitô, H., Kandori, H., Needleman, R., Lanyi, J. K., and Maeda, A. (1996) Biochemistry 35, 4063-4068]. The O-H stretching bands at 3671 cm-1 in the M intermediate and at 3654 cm-1 in the N intermediate are shown to originate from the same water molecule. It is located in the region surrounded by the Schiff base, Val49, Thr46, and Phe219 in the M intermediate, and moves closer to Val49 in the M to N reaction. The peptide C-N bond between Val49 and Pro50 and the C=O bond of Val49 undergo perturbations upon formation of the N intermediate but not the M and N-like MN states in which the Schiff base is unprotonated. The carbonyl oxygen of Val49 is proposed to be the acceptor in H-bonding with the protonated Schiff base in the N intermediate. The results suggest that water molecules may be involved in this interaction in the cytoplasmic region, and may play a role in the accessibility change of the Schiff base in the L to M to N photocycle steps.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: H
authors.initials: H
authors.lastname: Kandori
authors.forename: R
authors.initials: R
authors.lastname: Needleman
authors.forename: J K
authors.initials: JK
authors.lastname: Lanyi
authors.forename: A
authors.initials: A
authors.lastname: Maeda
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019617:Halobacterium salinarum / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010782:Photolysis; D011487:Protein Conformation; D011522:Protons; D012545:Schiff Bases; D017550:Spectroscopy, Fourier Transform Infrared; D014633:Valine / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D010455:Peptides; D011522:Protons; D012545:Schiff Bases; D014867:Water; D001436:Bacteriorhodopsins; D014633:Valine