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. 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 catalyze the first step in conjugated linoleic acid production. Proteins in this family act in an FAD dependent manner. The structure of a fatty acid double-bond hydratase from Lactobacillus acidophilus has been recently solved showing four structural domains.