Nucleotide triphosphates inhibit the degradation of unfolded proteins by HslV peptidase.
Escherichia coli HslVU is an ATP-dependent protease consisting of two heat shock proteins, the HslU ATPase and HslV peptidase. In the reconstituted enzyme, HslU stimulates the proteolytic activity of HslV by one to two orders of magnitude, while HslV increases the rate of ATP hydrolysis by HslU several-fold. Here we show that HslV alone can efficiently degrade certain unfolded proteins, such as unfolded lactalbumin and lysozyme prepared by complete reduction of disulfide bonds, but not their native forms. Furthermore, HslV alone cleaved a lactalbumin fragment sandwiched by two thioredoxin molecules, indicating that it can hydrolyze the internal peptide bonds of lactalbumin. Surprisingly, ATP inhibited the degradation of unfolded proteins by HslV. This inhibitory effect of ATP was markedly diminished by substitution of the Arg86 residue located in the apical pore of HslV with Gly, suggesting that interaction of ATP with the Arg residue blocks access of unfolded proteins to the proteolytic chamber of HslV. These results suggest that uncomplexed HslV is inactive under normal conditions, but may can degrade unfolded proteins when the ATP level is low, as it is during carbon starvation.
Lee
Jung Wook
JW
School of Biological Sciences, Seoul National University, Seoul 151-742, Korea.
Park
Eunyong
E
Bang
Oksun
O
Eom
Soo-Hyun
SH
Cheong
Gang-Won
GW
Chung
Chin Ha
CH
Seol
Jae Hong
JH
D049069:ATP-Dependent Proteases / Q000235:genetics / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002244:Carbon / Q000378:metabolism; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism; D006868:Hydrolysis; D007768:Lactalbumin / Q000378:metabolism; D008969:Molecular Sequence Data; D009113:Muramidase / Q000378:metabolism; D017510:Protein Folding
D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D002244:Carbon; D000255:Adenosine Triphosphate; D007768:Lactalbumin; D009113:Muramidase; D010450:Endopeptidases; D049069:ATP-Dependent Proteases; D000251:Adenosine Triphosphatases