Different Effects of Identical Symmetry-Related Mutations near the Bacteriochlorophyll Dimer in the Photosynthetic Reaction Center of Rhodobacter sphaeroides

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L. G. Vasilieva^1*, T. Y. Fufina¹, A. G. Gabdulkhakov², and V. A. Shuvalov¹

¹Institute of Basic Problems of Biology, 142290 Pushchino, Moscow Region, Russia; fax: (496) 733-0532; E-mail: vsyulya@mail.ru

²Institute of Protein Research, 142290 Pushchino, Moscow Region, Russia; fax: (495) 514-0218; E-mail: azat@vega.protres.ru

^* To whom correspondence should be addressed.

Received December 3, 2014; Revision received February 11, 2015

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In the bacterial photosynthetic reaction center (RC), asymmetric protein environment of the bacteriochlorophyll (BChl) dimer largely determines the photophysical and photochemical properties of the primary electron donor. Previously, we noticed significant differences in properties of Rhodobacter sphaeroides RCs with identical mutations in symmetry-related positions – I(M206)H and I(L177)H. The substitution I(L177)H resulted in covalent binding of BChl P_A with the L-subunit, as well as in 6-coordination of BChl B_B, whereas in RC I(M206)H no such changes of pigment–protein interactions were found. In addition, the yield of RC I(M206)H after its isolation from membranes was significantly lower than the yield of RC I(L177)H. This study shows that replacement of amino acid residues in the M203-M206 positions near BChls P_B and B_A by symmetry-related residues from the L-subunit near BChls P_A and B_B leads to further decrease in RC amount in the membranes associated obviously with poor assembly of the complex. Introduction of a new hydrogen bond between BChl P_B and its protein environment by means of the F(M197)H mutation stabilized the mutant RC but did not affect its low yield. We suggest that the mutation I(M206)H and substitution of amino acid residues in M203-M205 positions could disturb glycolipid binding on the RC surface near BChl B_A that is important for stable assembly of the complex in the membrane.

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KEY WORDS: bacterial photosynthesis, Rhodobacter sphaeroides, photosynthetic reaction center, site-directed mutagenesis, bacteriochlorophyll, magnesium atom coordination, pigment–protein interactions

DOI: 10.1134/S0006297915060012

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