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Publication Abstract from PubMed

The mesophilic purple sulfur phototrophic bacterium Allochromatium (Alc.) vinosum (bacterial family Chromatiaceae) has been a favored model for studies of bacterial photosynthesis and sulfur metabolism, and its core light-harvesting (LH1) complex has been a focus of numerous studies of photosynthetic light reactions. However, despite intense efforts, no high-resolution structure and thorough biochemical analysis of the Alc. vinosum LH1 complex have been reported. Here we present cryo-EM structures of the Alc. vinosum LH1 complex associated with reaction center (RC) at 2.24 A resolution. The overall structure of the Alc. vinosum LH1 resembles that of its moderately thermophilic relative Alc. tepidum in that it contains multiple pigment-binding alpha- and beta-polypeptides. Unexpectedly, however, six Ca ions were identified in the Alc. vinosum LH1 bound to certain alpha1/beta1- or alpha1/beta3-polypeptides through a different Ca(2+)-binding motif from that seen in Alc. tepidum and other Chromatiaceae that contain Ca(2+)-bound LH1 complexes. Two water molecules were identified as additional Ca(2+)-coordinating ligands. Based on these results, we reexamined biochemical and spectroscopic properties of the Alc. vinosum LH1-RC. While modest but distinct effects of Ca(2+) were detected in the absorption spectrum of the Alc. vinosum LH1 complex, a marked decrease in thermostability of its LH1-RC complex was observed upon removal of Ca(2+). The presence of Ca(2+) in the photocomplex of Alc. vinosum suggests that Ca(2+)-binding to LH1 complexes may be a common adaptation in species of Chromatiaceae for conferring spectral and thermal flexibility on this key component of their photosynthetic machinery.

High-resolution structure and biochemical properties of the LH1-RC photocomplex from the model purple sulfur bacterium, Allochromatium vinosum.,Tani K, Kanno R, Harada A, Kobayashi Y, Minamino A, Takenaka S, Nakamura N, Ji XC, Purba ER, Hall M, Yu LJ, Madigan MT, Mizoguchi A, Iwasaki K, Humbel BM, Kimura Y, Wang-Otomo ZY Commun Biol. 2024 Feb 12;7(1):176. doi: 10.1038/s42003-024-05863-w. PMID:38347078^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.