Identification of FkpA as a key quality control factor for the biogenesis of outer membrane proteins under heat shock conditions.

Journal of bacteriology

PubMedID: 24272780

Ge X, Lyu ZX, Liu Y, Wang R, Zhao XS, Fu X, Chang Z. Identification of FkpA as a key quality control factor for the biogenesis of outer membrane proteins under heat shock conditions. J Bacteriol. 2013;.
The outer membrane proteins (OMPs) of Gram-negative bacterial cells, as well as the mitochondrion and chloroplast organelles possess the unique and highly stable ß-barrel structures. Biogenesis of OMPs in Escherichia coli involves such periplasmic chaperones as SurA and Skp. Here, we found that the surA(-) skp(-) double deletion strain of E. coli, although lethal and defective in the biogenesis of OMPs at the normal growth temperature, is viable and effective at the heat shock temperature. We identified FkpA as the multicopy suppressor for the lethal phenotype of the surA(-) skp(-) strain. We also demonstrated that the deletion of fkpA from the surA(-) cells only resulted in a mild decrease in the levels of folded OMPs at the normal temperature but a severe decrease as well as lethality at the heat shock temperature, whereas the deletion of fkpA from the skp(-) cells had no detectable effect on the OMP biogenesis at both temperatures. These results strongly suggest a functional redundancy between FkpA and SurA for the OMP biogenesis at heat shock stress conditions. Mechanistically, we found that FkpA becomes a more efficient chaperone towards OMPs under the heat shock condition, with an increase in both binding rate and affinity. In light of these observations and earlier reports, we propose a temperature-responsive OMP biogenesis mechanism such that the functional importance of the three chaperones are such that SurA>Skp>FkpA at the normal temperature but FkpA=SurA>Skp at the heat shock temperature.