The MCRA (myosin-cross-reactive antigen) family of proteins were thought to have structural features in common with the beta chain of the class II antigens, as well as myosin, and may play an important role in the pathogenesis[1]. More recent work shows that these proteins act as hydratase enzymes that convert linoleic acid and oleic acid to their respective 10-hydroxy derivatives. It has been suggested that MCRA proteins catalyse the first step in conjugated linoleic acid production [2]. Proteins in this family act in an FAD dependent manner [3]. The structure of a fatty acid double-bond hydratase from Lactobacillus acidophilus has been recently solved showing four structural domains.

1: Cloning and sequence analysis of a gene encoding a 67-kilodalton myosin-cross-reactive antigen of Streptococcus pyogenes reveals its similarity with class II major histocompatibility antigens. Kil KS, Cunningham MW, Barnett LA; Infect Immun 1994;62:2440-2449. PMID:8188369

2: Myosin-cross-reactive antigens from four different lactic acid bacteria are fatty acid hydratases. Yang B, Chen H, Song Y, Chen YQ, Zhang H, Chen W; Biotechnol Lett. 2013;35:75-81. PMID:22955678

3: Myosin-cross-reactive antigen (MCRA) protein from Bifidobacterium breve is a FAD-dependent fatty acid hydratase which has a function in stress protection. Rosberg-Cody E, Liavonchanka A, Gobel C, Ross RP, O'Sullivan O, Fitzgerald GF, Feussner I, Stanton C; BMC Biochem. 2011;12:9. PMID:21329502

4: Myosin cross-reactive antigen of Streptococcus pyogenes M49 encodes a fatty acid double bond hydratase that plays a role in oleic acid detoxification and bacterial virulence. Volkov A, Liavonchanka A, Kamneva O, Fiedler T, Goebel C, Kreikemeyer B, Feussner I; J Biol Chem. 2010;285:10353-10361. PMID:20145247