Switching sides-Reengineered primary charge separation in the bacterial photosynthetic reaction center.

ABSTRACT: We report 90% yield of electron transfer (ET) from the singlet excited state P* of the primary electron-donor P (a bacteriochlorophyll dimer) to the B-side bacteriopheophytin (HB) in the bacterial photosynthetic reaction center (RC). Starting from a platform Rhodobacter sphaeroides RC bearing several amino acid changes, an Arg in place of the native Leu at L185-positioned over one face of HB and only ?4 Å from the 4 central nitrogens of the HB macrocycle-is the key additional mutation providing 90% yield of P+HB - This all but matches the near-unity yield of A-side P+HA - charge separation in the native RC. The 90% yield of ET to HB derives from (minimally) 3 P* populations with distinct means of P* decay. In an ?40% population, P* decays in ?4 ps via a 2-step process involving a short-lived P+BB - intermediate, analogous to initial charge separation on the A side of wild-type RCs. In an ?50% population, P* ? P+HB - conversion takes place in ?20 ps by a superexchange mechanism mediated by BB An ?10% population of P* decays in ?150 ps largely by internal conversion. These results address the long-standing dichotomy of A- versus B-side initial charge separation in native RCs and have implications for the mechanism(s) and timescale of initial ET that are required to achieve a near-quantitative yield of unidirectional charge separation.

SUBMITTER: Laible PD 

PROVIDER: S-EPMC6969525 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature