Cryo-EM structure of a Ca2+-bound photosynthetic LH1-RC complex containing multiple ??-polypeptides.

ABSTRACT: The light-harvesting-reaction center complex (LH1-RC) from the purple phototrophic bacterium Thiorhodovibrio strain 970 exhibits an LH1 absorption maximum at 960?nm, the most red-shifted absorption for any bacteriochlorophyll (BChl) a-containing species. Here we present a cryo-EM structure of the strain 970 LH1-RC complex at 2.82?Å resolution. The LH1 forms a closed ring structure composed of sixteen pairs of the ??-polypeptides. Sixteen Ca ions are present in the LH1 C-terminal domain and are coordinated by residues from the ??-polypeptides that are hydrogen-bonded to BChl a. The Ca2+-facilitated hydrogen-bonding network forms the structural basis of the unusual LH1 redshift. The structure also revealed the arrangement of multiple forms of ?- and ?-polypeptides in an individual LH1 ring. Such organization indicates a mechanism of interplay between the expression and assembly of the LH1 complex that is regulated through interactions with the RC subunits inside.

SUBMITTER: Tani K 

PROVIDER: S-EPMC7532537 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature