In bacterial reaction centers, a key residue suppresses mutational blockage of two different proton transfer steps
Article
Miksovska, J, Valerio-Lepiniec, M, Schiffer, M et al. (1998). In bacterial reaction centers, a key residue suppresses mutational blockage of two different proton transfer steps
. BIOCHEMISTRY, 37(8), 2077-2083. 10.1021/bi972696n
Miksovska, J, Valerio-Lepiniec, M, Schiffer, M et al. (1998). In bacterial reaction centers, a key residue suppresses mutational blockage of two different proton transfer steps
. BIOCHEMISTRY, 37(8), 2077-2083. 10.1021/bi972696n
In reaction centers of Rhodobacter (Rb.) capsulatus, the M43Asn → Asp substitution is capable of restoring rapid rates for delivery of the second proton to Q(B) in a mutant that lacks L212Glu. Flash-induced absorbance spectroscopy was used to show a nearly native rate for transfer of the second proton to Q(B) (≃ 700 s-1) in the L212Gln+M43Asp double-mutant reaction center; this rate was shown to decrease more than 1000-fold in the photoincompetent L212Glu → Gln mutant [Miksovska, J., Kalman, L., Maroti, P., Schiffer, M., Sebban, P., and Hanson, D. K. (1997) Biochemistry 36, 12216-12226]. In Rb. sphaeroides, the equivalent M44Asn → Asp mutation was reported to restore the rate of transfer of the first proton to a wild-type level when it is added to the L213Asp → Ash photoincompetent mutant [Rongey, S. H., Paddock, M. L., Feher, G., and Okamura, M. Y. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 1325-1329]. It is remarkable that the same second-site mutation can compensate for both of these mutations which severely impair reaction center function by blocking two different proton-transfer reactions. We suggest that residue M43Asp is situated in a key position which can link pathways for delivery of both the first and second protons (involving structured water molecules) to Q(B).
