4g4e
Crystal structure of the L88A mutant of HslV from Escherichia coli
Structural highlights
FunctionHSLV_ECOLI Protease subunit of a proteasome-like degradation complex believed to be a general protein degrading machinery. The complex has been shown to be involved in the specific degradation of heat shock induced transcription factors such as RpoH and SulA. In addition, small hydrophobic peptides are also hydrolyzed by HslV. HslV has weak protease activity even in the absence of HslU, but this activity is induced more than 100-fold in the presence of HslU. HslU recognizes protein substrates and unfolds these before guiding them to HslV for hydrolysis. HslV is not believed to degrade folded proteins.[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedIn all cells, ATP-dependent proteases play central roles in the controlled degradation of short-lived regulatory or misfolded proteins. A hallmark of these enzymes is that proteolytic active sites are sequestered within a compartmentalized space, which is accessible to substrates only when they are fed into the cavity by protein-unfolding ATPases. HslVU is a prototype of such enzymes, consisting of the hexameric HslU ATPase and the dodecameric HslV protease. HslV forms a barrel-shaped proteolytic chamber with two constricted axial pores. Here, we report that structural alterations of HslV's pore motif dramatically affect the proteolytic activities of both HslV and HslVU complexes. Mutations of a conserved pore residue in HslV (Leu88 to Ala, Gly, or Ser) led to a tighter binding between HslV and HslU and a dramatic stimulation of both the proteolytic and ATPase activities. Furthermore, the HslV mutants alone showed a marked increase of basal hydrolytic activities toward small peptides and unstructured proteins. A synthetic peptide of the HslU C-terminal tail further stimulated the proteolytic activities of these mutants, even allowing degradation of certain folded proteins in the absence of HslU. Moreover, expression of the L88A mutant in Escherichia coli inhibited cell growth, suggesting that HslV pore mutations dysregulate the protease through relaxing the pore constriction, which normally prevents essential cellular proteins from random degradation. Consistent with these observations, an X-ray crystal structure shows that the pore loop of L88A-HslV is largely disordered. Collectively, these results suggest that substrate degradation by HslV is controlled by gating of its pores. Structural Alteration in the Pore Motif of the Bacterial 20S Proteasome Homolog HslV Leads to Uncontrolled Protein Degradation.,Park E, Lee JW, Yoo HM, Ha BH, An JY, Jeon YJ, Seol JH, Eom SH, Chung CH J Mol Biol. 2013 May 21. pii: S0022-2836(13)00310-0. doi:, 10.1016/j.jmb.2013.05.011. PMID:23707406[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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