This domain is found at the C-terminal end of Transcriptional regulator from Lactococcus lactis (YgfC, also known as heme- regulated transporter regulator, HrtR) and similar proteins predominantly from firmicutes. YgfC senses and binds a heme molecule to regulate the expression of the heme-efflux system responsible for heme homeostasis in this bacteria. This member of the TetR family of transcriptional regulators shows two helical domains and adopts a dimeric configuration [1]. This entry represents the heme-sensing (heme-binding) domain, which contains the alpha-helices that form the four-helix bundle that constitutes a dimer interface.

1: Structural basis for the transcriptional regulation of heme homeostasis in Lactococcus lactis. Sawai H, Yamanaka M, Sugimoto H, Shiro Y, Aono S; J Biol Chem. 2012;287:30755-30768. PMID:22798069