Identifying New Factors in Outer Membrane Protein Assembly in Escherichia coli
Charlson, Emily and Misra, Rajeev
School of Life Sciences, Arizona State University
The assembly and integration of proteins in the outer membrane of Escherichia coli is essential in maintaining proper cell permeability. A recently discovered protein complex located in the outer membrane comprised of two essential proteins, YfiO and YaeT, and two nonessential proteins, NlpB and YfgL has been shown to facilitate the insertion of proteins into the outer membrane. Past work has described the role of a nonessential lipoprotein component of the complex, YfgL, in the outer membrane protein (OMP) assembly process. Current studies focus on identifying new factors in OMP assembly using an OMP assembly-deficient strain of Escherichia coli, cyfgL cdegP. In our recent paper (Charlson et al. 2006), we described the conditional lethality of the cyfgL cdegP mutation and suggest that the various defects of this strain, including a sensitivity to the antibiotic vancomycin and an inability to grow at temperatures above 30_C, derives from a severely compromised outer membrane barrier and the toxic accumulation of unfolded OMP assembly intermediates that are clogging the assembly pathways of a YfgL-deficient OMP assembly apparatus. Selecting for suppressors of the cyfgL cdegP mutation that overcome the assembly defects of this strain by either growing in the presence of vancomycin, at high temperatures, or both, has yielded several classes of suppressor mutations that affect OMP assembly in strikingly different ways, suggesting that the defects of the cyfgL cdegP mutation can be overcome by more than one mechanism. The identification and characterization of these mutations can identify novel factors that either directly or indirectly affect OMP biogenesis.