9.B.357.  The Bacterial Envelope Biogenesis (BEB) Family 

The bacterial cytoplasmic membrane is a principal site of protein translocation, lipid and peptidoglycan biogenesis, signal transduction, transporters and energy generating components of the respiratory chain. 25-30% of bacterial proteomes consist of membrane proteins.  Mychack et al. 2019 showed that YciB (IspZ) and DcrB (YhhR), two small cytoplasmic membrane proteins, play an essential synergistic role in maintaining cell envelope integrity of E. coli. Lack of both YciB and DcrB results in pleiotropic cell defects including increased levels of lipopolysaccharide, membrane vesiculation, and dynamic shrinking and extension of the cytoplasmic membrane accompanied by lysis and cell death. The stalling of an abundant outer membrane lipoprotein, Lpp, at the periplasmic face of the inner membrane leads to lethal inner membrane-peptidoglycan linkages. Additionally, the periplasmic chaperone Skp contributes to yciB dcrB mutant cell death possibly by mistargeting stalled porins into the inner membrane. Consistent with the idea of a compromised envelope in the yciB dcrB mutant, multiple envelope stress response systems are induced, with Cpx signal transduction being required for growth. These results suggest a fundamental role for YciB and DcrB in cell envelope biogenesis.

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