Activation of DegP chaperone-protease via formation of large cage-like oligomers upon binding to substrate proteins

Abstract

Cells use molecular chaperones and proteases to implement the essential quality control mechanism of proteins. The DegP (HtrA) protein, essential for the survival of Escherichia coli cells at elevated temperatures with homologues found in almost all organisms uniquely has both functions. Here we report a mechanism for DegP to activate both functions via formation of large cage-like 12-and 24-mers after binding to substrate proteins. Cryo-electron microscopic and biochemical studies revealed that both oligomers are consistently assembled by blocks of DegP trimers, via pairwise PDZ1-PDZ2 interactions between neighboring trimers. Such interactions simultaneously eliminate the inhibitory effects of the PDZ2 domain. Additionally, both DegP oligomers were also observed in extracts of E. coli cells, strongly implicating their physiological importance.cryo-electron microscopy ͉ protein quality control ͉ HtrA ͉ PDZ domain ͉ oligomerization

Salmonella enterica Serovar Typhimurium HtrA: regulation of expression and role of the chaperone and protease activities during infection

“…However, HtrA DPDZ2 could not complement the temperature-sensitive phenotype of an E. coli htrA mutant and the HtrA DPDZ1 protein could partially complement if induced to very high levels (Spiess et al, 1999). HtrA in the periplasm has recently been shown to form large multimeric cage-like structures that are the functional form of the protein in vivo (Jiang et al, 2008;Krojer et al, 2008). Interaction between the PDZ domains on the different HtrA subunits is important for oligomerization (Jiang et al, 2008;Krojer et al, 2008).…”

“…HtrA in the periplasm has recently been shown to form large multimeric cage-like structures that are the functional form of the protein in vivo (Jiang et al, 2008;Krojer et al, 2008). Interaction between the PDZ domains on the different HtrA subunits is important for oligomerization (Jiang et al, 2008;Krojer et al, 2008). Therefore it is possible that the HtrA variants that lack either of the PDZ domains do not complement the growth of a S. Typhimurium mutant in vitro or in vivo because they cannot form multimeric HtrA.…”

Unfolded protein responses in bacteria and mitochondria: A central role for the ClpXP machine

“…Collectively, the upregulation of these factors acts to re-establish protein homeostasis and envelope integrity. For example, the periplasmic protein DegP is upregulated on envelope stress and undergoes oligomerization and activation in the presence of unfolded protein, assisting the removal of the damaged proteins by repair or proteolysis (40,42,43). So how is the unfolded protein stress signal sensed and transmitted across the membrane?…”

Cryo-EM structure of Nma111p, a unique HtrA protease composed of two protease domains and four PDZ domains

“…Based on the domain organization, the HtrA family proteins can be divided into distinct groups. Group 1 proteins (e.g., DegS in E. coli and Htra2 in mammal) contain one protease domain and one PDZ domain [4,5], and group 2 proteins (e.g., DegP and DegQ in E. coli) contain one protease domain and two PDZ domains [6,7]. Nma111p-like proteases in group 3 are distinctively characterized by possessing two protease domains and four PDZ domains, of which the N-terminal protease domain exhibits protease activity, whereas the C-terminal protease domain is supposed to be degenerated in protease activity.…”

“…The structures of several members of groups 1 and 2 of the HtrA family have been determined by X-ray crystallography or cryo-electron microscopy (cryo-EM) [6,7,9,10]. However, none belongs to group 3.…”