Family members were previously thought to be ArgK proteins acting as ATPase enzymes and kinases. They are now believed to be methylmalonyl Co-A mutase-associated GTPase MeaB. Structural studies of MeaB and the human ortholog (methylmalonyl associated protein A) MMAA, reveal alpha-helical domains at the N- and C-termini as well as a Ras-like GTPase domain. Mutational analysis of MeaB, show prohibited growth in Methylobacterium due to the inability to convert methylmalonyl-CoA to succinyl-CoA caused by an inactive form of methylmalonyl-CoA mutatase (mcm). In humans, mutations in (MMAA) are associated with the fatal disease methylmalonyl aciduria [1].

1: Crystal structures of Mycobacterial MeaB and MMAA-like GTPases. Edwards TE, Baugh L, Bullen J, Baydo RO, Witte P, Thompkins K, Phan IQ, Abendroth J, Clifton MC, Sankaran B, Van Voorhis WC, Myler PJ, Staker BL, Grundner C, Lorimer DD; J Struct Funct Genomics. 2015;16:91-99. PMID:25832174