Shp is part of a complex which functions in heme uptake in Streptococcus pyogenes. During which, Shp transfers its heme to HtsA which is a component of an ABC transporter. The heme binding region of Shp contains an immunoglobulin-like beta-sandwich fold and has a unique heme-iron coordination with the axial ligands being two methionine residues from the same Shp molecule [1]. Surrounding the heme pocket, there is a negative surface which may serve as a docking interface for heme transfer [1].

1: Bis-methionyl coordination in the crystal structure of the heme-binding domain of the streptococcal cell surface protein Shp. Aranda R 4th, Worley CE, Liu M, Bitto E, Cates MS, Olson JS, Lei B, Phillips GN Jr; J Mol Biol. 2007;374:374-383. PMID:17920629