This family of proteins represents HapK, a protein of unknown function, with two homologues PigK and RedY. The monomer structure of the protein contains a four-stranded anti parallel beta-sheet, three alpha-helices and a short C terminal tail which it uses for dimer formation [1]. The surface of HapK has a deep cavity with consists of a kinked helix and a beta-four strand. HapK could be involved in prodigiosin biosynthesis, specifically the binding of a bipyrrole intermediate such as HBM or MBM [1].

1: Structural insight of the role of the Hahella chejuensis HapK protein in prodigiosin biosynthesis. Cho HJ, Kim KJ, Kim MH, Kang BS; Proteins. 2008;70:257-262. PMID:17729271