This presumed domain is about 100 amino acids in length. It is found in lipoprotein of unknown function and is greatly expanded in Mycoplasma pulmonis. The domain is found in up to five copies in some proteins. This family also includes the Mycoplasma arthritidis MAA2 variable surface protein. MAA2 is implicated in in cytoadherence and virulence and has been shown to exhibit both size and phase variability.