New functional identity of the essential inner membrane protein YejM: the cardiolipin translocator is also a metalloenzyme

Recent recurrent outbreaks of Gram-negative bacteria show the critical need to target essential bacterial mechanisms to fight the increase of antibiotic resistance. Pathogenic Gram-negative bacteria have developed several strategies to protect themselves against the host immune response and antibiotics. One strategy is to remodel the outer membrane where several genes are involved. yejM was discovered as an essential gene in E. coli and S. typhimurium that plays a critical role in their virulence by changing the outer membrane permeability by translocating and increasing the cardiolipin lipid concentration. How the inner membrane protein YejM with its periplasmic domain acts as a cardiolipin translocator remains unknown. Despite overwhelming structural similarity of the periplasmic domains of two YejM homologues with hydrolases like arylsulfatases, no enzymatic activity has been reported for YejM. Our studies reveal an intact active site with bound metal ions in the structure of YejM periplasmic domain. Furthermore, we show that YejM has a phosphatase activity that is dependent on the presence of magnesium ions and is linked to its cardiolipin translocation properties. Understanding the molecular mechanism by which YejM is involved in OM remodeling will help to identify a new drug target in the fight against the increased antibiotic resistance.