Protein changes associated with reprotonation of the Schiff base in the photocycle of Asp96-->Asn bacteriorhodopsin. The MN intermediate with unprotonated Schiff base but N-like protein structure.
The difference Fourier transform infrared spectrum for the N intermediate in the photoreaction of the light-adapted form of bacteriorhodopsin can be recorded at pH 10 at 274 K (Pfefferlé, J.-M., Maeda, A., Sasaki, J., and Yoshizawa, T. (1991) Biochemistry 30, 6548-6556). Under these conditions, Asp96-->Asn bacteriorhodopsin gives a photoproduct which shows changes in protein structure similar to those observed in N of wild-type bacteriorhodopsin. However, decreased intensity of the chromophore bands and the single absorbance maximum at about 400 nm indicate that the Schiff base is unprotonated, as in the M intermediate. This photoproduct was named MN. At pH 7, where the supply of proton is not as restricted as at pH 10, Asp96-->Asn bacteriorhodopsin yields N with a protonated Schiff base. The Asn96 residue, which cannot deprotonate as Asp96 in wild-type bacteriorhodopsin, is perturbed upon formation of both MN at pH 10 and N at pH 7. We suggest that the reprotonation of the Schiff base is preceded by a large change in the protein structure including perturbation of the residue at position 96.
Sasaki
J
J
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Shichida
Y
Y
Lanyi
J K
JK
Maeda
A
A
D001216:Asparagine; D001224:Aspartic Acid; D001436:Bacteriorhodopsins / Q000737:chemistry / Q000378:metabolism*; D005583:Fourier Analysis; D019617:Halobacterium salinarum / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D012545:Schiff Bases; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared
D011994:Recombinant Proteins; D012545:Schiff Bases; D001224:Aspartic Acid; D001436:Bacteriorhodopsins; D001216:Asparagine