The chaperone-assisted membrane release and folding pathway is sensed by two signal transduction systems

Abstract

The assembly of interactive protein subunits into extracellular structures, such as pilus fibers in the Enterobacteriaceae, is dependent on the activity of PapD-like periplasmic chaperones. The ability of PapD to undergo a β zippering interaction with the hydrophobic C-terminus of pilus subunits facilitates their folding and release from the cytoplasmic membrane into the periplasm. In the absence of the chaperone, subunits remained tethered to the membrane and were driven off-pathway via non-productive interactions. These offpathway reactions were detrimental to cell growth; wild-type growth was restored by co-expression of PapD. Subunit misfolding in the absence of PapD was sensed by two parallel pathways: the Cpx twocomponent signaling system and the σE modulatory pathway.

FimK regulation on the expression of type 1 fimbriae in Klebsiella pneumoniae CG43S3

“…Decreased expression of type 1 fimbriae was reported for the E. coli K1 ompA deletion mutant (Teng et al, 2006). Misfolding of the P fimbriae subunit triggered the 2CS Cpx and s E regulatory pathways (Jones et al, 1997). These studies suggest that deleting mrkA may change the outer-membrane protein pattern or trigger an envelope stress system, leading to the expression of type 1 fimbriae in K. pneumoniae CG43S3.…”

The extracytoplasmic adaptor protein CpxP is degraded with substrate by DegP

“…Overnight cultures were grown in the appropriate antibiotic and subcultured to OD 600 Ϸ 0.05 in 7 ml of fresh LB medium and grown at 37°C for 1 h. Cells containing isopropyl-␤-D-thiogalactopyranoside (IPTG)-inducible plasmids were then induced with either 10 M (toxicity, subunit accumulation in wild-type) or 0.5 mM (proteolysis, subunit accumulation in cpxA24 derivatives) IPTG and grown at 37°C. A lower IPTG concentration was used for toxicity assays on cpxRA ϩ cells because at the higher IPTG concentration, misfolded PapE or PapG expression is similarly toxic irrespective of the degP genotype (10). The OD 600 of all cultures were recorded preinduction and at multiple time intervals after induction for 2 h. Samples were removed at each interval, normalizing for the number of cells per milliliter, and harvested by centrifugation.…”

“…To gain insight into the function of CpxP, we examined the toxicity associated with expressing either the PapE pilin subunit or the PapG adhesin in the absence of its chaperone. In wild-type strains, expression of either papE or papG is toxic (10). Cell growth is inhibited in Ͻ 1 h after the induction of PapE synthesis, even with low concentrations of inducer (10 M) ( Fig.…”

“…In the absence of PapD, the tip fibrillar subunit PapE and the adhesin PapG misfold. Misfolded forms of PapE and PapG are toxic, and they are potent inducers of the Cpx stress response (10).…”

Unraveling the molecular basis of subunit specificity in P pilus assembly by mass spectrometry

“…Here, the same periplasmic chaperone binds each subunit, capping its interactive surfaces and maintaining it in an assembly-competent conformation (Fig. 1A) (6)(7)(8). The chaperone-subunit complexes are then taken to a site of assembly consisting of an outer-membrane protein, the ''usher,'' where the chaperone is released and subunit polymerization occurs ( Fig.…”