The Hb-interacting domain (HID) is found duplicated in Heme-binding protein Shr from Streptococcus pyogenes, a potentially lethal human pathogen, and in one to six copies in other uncharacterised bacterial proteins. Shr is a virulence factor that captures Hb and binds to the oxidized form of heme through an N-terminal region that contains two copies of this domain. HID shows a beta-sandwich-type fold in which two antiparallel beta-sheets are flanked by an alpha-helix [1].

1: The Streptococcus pyogenes Shr protein captures human hemoglobin using two structurally unique binding domains. Macdonald R, Cascio D, Collazo MJ, Phillips M, Clubb RT; J Biol Chem. 2018;293:18365-18377. PMID:30301765