High-light-inducible proteins HliA and HliB: pigment binding and protein-protein interactions

ABSTRACT: High-light-inducible proteins (Hlips) are single-helix transmembrane proteins that are essential for the survival of cyanobacteria under stress conditions. The model cyanobacterium Synechocystis sp. PCC 6803 contains four Hlip isoforms (HliA-D) that associate with Photosystem II (PSII) during its assembly. HliC and HliD are known to form pigmented (hetero)dimers that associate with the newly synthesized PSII reaction center protein D1 in a configuration that allows thermal dissipation of excitation energy. Thus, it is expected that they photoprotect the early steps of PSII biogenesis. HliA and HliB, on the other hand, bind the PSII inner antenna protein CP47 but the mode of interaction and pigment binding have not been resolved. Here, we isolated His-tagged HliA and HliB from Synechocystis and show that these two very similar Hlips are not interacting with each other as anticipated but they form HliAC and HliBC heterodimers. Both dimers bind Chl and ?-carotene in a quenching conformation and associate with the CP47 assembly module as well as with later PSII assembly intermediates containing CP47. In the absence of HliC, the cellular levels of HliA and HliB reduced and both bound defectively to HliD. We postulate a model in which HliAC, HliBC and HliDC dimers are the functional Hlip units in Synechocystis. The smallest Hlip, HliC, acts as a ?generalist? providing the second copy of the Chl-binding motif, while the N-terminus of ?specialists? (HliA, B or D) dictates interaction with other proteins. In this way, HliC also prevents unspecific dimerization of Hlip-associated PSII-assembly intermediates.

INSTRUMENT(S): timsTOF Pro

ORGANISM(S): Synechocystis Sp. Pcc 6803 (ncbitaxon:1148)

SUBMITTER: Minna Maria Konert  

PROVIDER: MSV000088753 | MassIVE | Mon Jan 31 09:03:00 GMT 2022

SECONDARY ACCESSION(S): PXD031369

REPOSITORIES: MassIVE