The Yeast HtrA Orthologue Ynm3 Is a Protease with Chaperone Activity that Aids Survival Under Heat Stress

Abstract

Ynm3 is the only budding yeast protein possessing a combination of serine protease and postsynaptic density 95/disclarge/zona occludens domains, a defining feature of the high temperature requirement A (HtrA) protein family. The bacterial HtrA/DegP is involved in protective stress response to aid survival at higher temperatures. The role of mammalian mitochondrial HtrA2/Omi in protein quality control is unclear, although loss of its protease activity results in susceptibility toward Parkinson's disease, in which mitochondrial dysfunction and impairment of protein folding and degradation are key pathogenetic features. We studied the role of the budding yeast HtrA, Ynm3, with respect to unfolding stresses. Similar to Escherichia coli DegP, we find that Ynm3 is a dual chaperone-protease. Its proteolytic activity is crucial for cell survival at higher temperature. Ynm3 also exhibits strong general chaperone activity, a novel finding for a eukaryotic HtrA member. We propose that the chaperone activity of Ynm3 may be important to improve the efficiency of proteolysis of aberrant proteins by averting the formation of nonproductive toxic aggregates and presenting them in a soluble state to its protease domain. Suppression studies with ⌬ynm3 led to the discovery of chaperone activity in a nucleolar peptidyl-prolyl cis-trans isomerase, Fpr3, which could partly relieve the heat sensitivity of ⌬ynm3.

Nuclear localisation is crucial for the proapoptotic activity of the HtrA-like serine protease Nma111p

“…The active catalytic serine of trypsin-like serine proteases is typically embedded in a sequence motif GNSGG as consensus (Clausen et al, 2002;Pallen and Wren, 1997), which, in Nma111p, is 234GSSGS238, accordingly. We have previously shown that a mutation in S235 inhibits the ability of Nma111p to promote cell death (Fahrenkrog et al, 2004), whereas others have recently shown that mutation of S236 impairs its chaperone activity (Padmanabhan et al, 2009). Consistent with our previous data, we found here that cells that express ProtA-Nma111p-N with a cysteine mutation at S235 are less sensitive to oxidative-stress-and ageing-induced apoptosis than cells expressing a wild-type supplementary material Figs S5 and S6).…”

“…Therefore, S235 is unambiguously important for the proapoptotic activity of Nma111p. The controversy between our data and that of Padmanabhan et al (Padmanabhan et al, 2009) most probably arises from the different strain background used. Whereas in our background, i.e.…”

“…In addition, this protein is implicated in lipid homeostasis and exhibits chaperone activity (Padmanabhan et al, 2009;Tong et al, 2006). In this context, both the apoptotic and the chaperone activity of Nma111p depend on its serine-protease activity, although the actual catalytic serine has remained controversial (Fahrenkrog et al, 2004;Padmanabhan et al, 2009).…”

HtrA, a Temperature- and Stationary Phase-Activated Protease Involved in Maturation of a Key Microbial Virulence Determinant, Facilitates Borrelia burgdorferi Infection in Mammalian Hosts

“…Here, we propose a critical role for BbHtrA, a high-temperature-induced protease, in the cellular regulation and stress tolerance of Lyme disease spirochetes. A similar high-temperature sensitivity of HtrA deletion mutants has also been observed in other organisms such as Escherichia coli and Saccharomyces cerevisiae (50,51). Interestingly, despite the presence of BbhtrA as a single gene, the generation of deletion mutants with growth kinetics similar to those of WT spirochetes, especially at 34°C, suggests that its role is nonessential, at least in the in vitro growth of the organism.…”

Mitochondrial Protein Quality Control: The Mechanisms Guarding Mitochondrial Health

“…Such molecular architecture also permits chaperonelike functions of AAA + proteases and appears to confer the ability to recognize misfolded or unassembled proteins and refold, and/or extract these polypeptides from phospholipid bilayers (159). The second group of proteases is more heterogeneous and includes the following: (i) processing peptidases (MPP, Oct1, Icp55, Cym1, and IMP) involved in sequential removal and/or degradation of mitochondrial targeting sequences (MTS) and thus proper biogenesis, sorting, and stabilization of matrix-and IM-targeted proteins (3, 73,92,131,133,176,185); (ii) soluble peptidases (Prd1/Neurolysin, Atp23, and Ynm3/Omi) that seemingly contribute to MQC in the IMS (92,143,145,180,199); and (iii) IM-bound proteases (Pcp1/PARL, Oma1) implicated in the quality control of the IM proteome and regulation of mitochondrial dynamics (8,19,54,58,78,83,97,127).…”