2.A.127.1.1
PbgA (YejM) of 586 aas and 5 N-terminal TMSs with a C-terminal alkaline phosphatase-like domain (Dalebroux et al. 2015). The globular domains of PbgA resemble the structures of the arylsulfatase protein family and contains a novel core hydrophobic pocket that may be responsible for binding and transporting cardiolipin (Dong et al. 2016).  PhoPQ is activated within the intracellular phagosome environment of the host animal, where it promotes remodeling of the outer membrane and resistance to innate immune antimicrobial peptides. Maintenance of the PhoPQ-regulated outer membrane barrier requires PbgA, an inner membrane protein with a transmembrane domain essential for growth, and a periplasmic domain required for PhoPQ-activated increases in outer membrane cardiolipin. Fan et al. 2020 reported the crystal structure of cardiolipin-bound PbgA, adopting a transmembrane fold that features a cardiolipin binding site in close proximity to a long and deep cleft spanning the lipid bilayer. The end of the cleft extends into the periplasmic domain of the protein, which is structurally coupled to the transmembrane domain via a functionally critical C-terminal helix. In conjunction with a conserved putative catalytic dyad situated at the middle of the cleft, structural and mutational analyses suggest that PbgA is a multifunction membrane protein that mediates cardiolipin transport, a function essential for growth, and perhaps catalysis of an unknown enzymatic reaction (Fan et al. 2020).