Publications by authors named "Gregory A Tira"
The rates, yields, mechanisms and directionality of electron transfer (ET) are explored in twelve pairs of Rhodobacter (R.) sphaeroides and R. capsulatus mutant RCs designed to defeat ET from the excited primary donor (P*) to the A-side cofactors and re-direct ET to the normally inactive mirror-image B-side cofactors.
View Article and Find Full Text PDFThe primary electron transfer (ET) processes at 295 and 77 K are compared for the reaction center (RC) pigment-protein complex from 13 mutants including a wild-type control. The engineered RCs bear mutations in the L and M polypeptides that largely inhibit ET from the excited state P* of the primary electron donor (P, a bacteriochlorophyll dimer) to the normally photoactive A-side cofactors and enhance ET to the C-symmetry related, and normally photoinactive, B-side cofactors. P* decay is multiexponential at both temperatures and modeled as arising from subpopulations that differ in contributions of two-step ET ( P* → PB → PH), one-step superexchange ET ( P* → PH), and P* → ground state.
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- All natural amino acids were tested for substitution at position L185 near the B-side bacteriopheophytin in bacterial reaction centers, resulting in various modifications.
- Approximately 50% of the reaction centers with Glu at L185 incorporated a magnesium chlorin with unique properties rather than the typical BChl oxidation product, leading to the formation of a charge-separated state in some cases.
- Different amino acid substitutions yielded varying amounts of bacteriochlorophyll (BChl) in the reaction centers, revealing new insights into how amino acids can influence pigment types in photosynthetic proteins.
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 (H) in the bacterial photosynthetic reaction center (RC). Starting from a platform RC bearing several amino acid changes, an Arg in place of the native Leu at L185-positioned over one face of H and only ∼4 Å from the 4 central nitrogens of the H macrocycle-is the key additional mutation providing 90% yield of PH This all but matches the near-unity yield of A-side PH charge separation in the native RC. The 90% yield of ET to H derives from (minimally) 3 P* populations with distinct means of P* decay.
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