Structural characterization of a zinc-coordinated bis-histidine heme-binding site in the DUF2470 cyanobacterial protein

A large family of domain of unknown function (DUF) -containing proteins was recently identified by phylogenomic studies to bind to heme. DUF2470 and related subfamilies of phototroph-specific homologs have diverse heme -related functions, but the structure-function link of DUF2470 itself had yet to be determined. In Synechocystis, DUF2470 forms single domain proteins and were discovered to bind heme and zinc ions, generating a unique two - fold symmetric, zinc-bound bis-histidine heme site. Structural and spectroscopic characterizations of the wild -type and variants lacking conserved histidine residues elucidate the importance of zinc-binding and histidine residues fo r heme-binding activity. Results here supplement in vivo experiments and observed phenotypes that implicate DUF2470 in heme-dependent regulation of electron transport chains.