Role for Skp in LptD Assembly in Escherichia coli

Abstract

ABSTRACT The periplasmic chaperone Skp has long been implicated in the assembly of outer membrane proteins (OMPs) in Escherichia coli . It has been shown to interact with unfolded OMPs, and the simultaneous loss of Skp and the main periplasmic chaperone in E. coli , SurA, results in synthetic lethality. However, a Δ skp mutant displays only minor OMP assembly defects, and no OMPs have been shown to require Skp for their assembly. Here, we report a role for Skp in the assembly of the essential OMP LptD. This role may be compensated for by other OMP assembly proteins; in the absence of both Skp and FkpA or Skp and BamB, LptD assembly is impaired. Overexpression of SurA does not restore LptD levels in a Δ skp Δ fkpA double mutant, nor does the overexpression of Skp or FkpA restore LptD levels in the Δ surA mutant, suggesting that Skp acts in concert with SurA to efficiently assemble LptD in E. coli . Other OMPs, including LamB, are less affected in the Δ skp Δ fkpA and Δ skp bamB :: kan double mutants, suggesting that Skp is specifically necessary for the assembly of certain OMPs. Analysis of an OMP with a domain structure similar to that of LptD, FhuA, suggests that common structural features may determine which OMPs require Skp for their assembly.