Characteristics of light-harvesting complex II mutant of <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis> with alterations at the transmembrane helices of β-subunit

The peripheral light-harvesting complex II (LHII) is an important component of the photosynthetic apparatus of Rhodobacter sphaeroides. In this study, genetic, biochemical, and spectroscopic approaches were applied to investigate the spectral properties and functions of LHII in which two amino acid residues Phe32 and Leu42 in the transmembrane helix domain of pucB-encoded β-apoprotein were replaced by Leu and Pro. The mutated LHII complex showed blue shift of absorbance peaks in the near infrared region at ∼801–845 nm in R. sphaeroides. It should be noted that the B800 peak was much lower than that of the native LHII, and transfer energy was efficient from the B800 to the B850 pigments in the LHII complex. The results suggest that the mutated pucB could be expressed in R. sphaeroides, and the functional LHII was assembled into the membrane of R. sphaeroides notwithstanding with the different spectral properties. These mutated residues were indeed critical for the modulation of characteristics and function of LHII complex. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 7, pp. 993–999.