INTERACTION OF THE PROTONATED SCHIFF-BASE WITH THE PEPTIDE BACKBONE OF VALINE-49 AND THE INTERVENING WATER MOLECULE IN THE N PHOTOINTERMEDIATE OF BACTERIORHODOPSIN
Y. Yamazaki et al., INTERACTION OF THE PROTONATED SCHIFF-BASE WITH THE PEPTIDE BACKBONE OF VALINE-49 AND THE INTERVENING WATER MOLECULE IN THE N PHOTOINTERMEDIATE OF BACTERIORHODOPSIN, Biochemistry, 37(6), 1998, pp. 1559-1564
The effects of replacing Val49, Thr46, Asp96, and Phe219 in the cytopl
asmic 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 M-N intermediates. This study is an extensio
n of previous work on the L photointermediate [Yamazaki, Y., Tuzi, S.,
Saito, H., Kandori, H., Needleman, R., Lanyi, J. K., and Maeda, A. (1
996) 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 un
dergo perturbations upon formation of the N intermediate but not the M
and N-like M-N states in which the Schiff base is unprotonated. The c
arbonyl oxygen of Val49 is proposed to be the acceptor in H-bonding wi
th the protonated Schiff base in the N intermediate. The results sugge
st that water molecules may be involved in this interaction in the cyt
oplasmic region, and may play a role in the accessibility change of th
e Schiff base in the L to M to N photocycle steps.