title: Isolation and characterization of the phage T4 PinA protein, an inhibitor of the ATP-dependent lon protease of Escherichia coli.
abstract: The bacteriophage T4 PinA protein, expression of which leads to inhibition of protein degradation in Escherichia coli cells, has been purified from cells carrying multiple copies of the pinA gene. PinA is a heat-stable protein with a subunit Mr of 18,800 and an isoelectric point of 4.6. Under nondenaturing conditions on a gel filtration column, PinA migrated in two peaks corresponding to a dimer and a tetramer. Purified PinA inhibited ATP-dependent protein degradation by Lon protease in vitro; it did not inhibit the activity of other E. coli ATP-dependent proteases, ClpAP or ClpYQ. Furthermore, PinA did not inhibit ATP-independent proteolysis in E. coli cell extracts. PinA binds with high affinity to Lon protease (Kd approximately 10 nM for dimer binding), and a complex with approximately 1 dimer of PinA per tetramer of Lon protease could be isolated by gel filtration. Lon activity was partially restored upon dilution of the PinA-Lon complex to subnanomolar concentrations, indicating that inhibition was reversible and that PinA did not covalently modify Lon protease. PinA was not cleaved by Lon protease, and heating the Lon-PinA complex at 65 degrees C denatured Lon protease and released active PinA. The properties of PinA in vitro suggest that PinA inhibits protein degradation in vivo by forming a tight, reversible complex with Lon protease.
authors.affiliation: Waksman Institute, Rutgers, The State University of New Jersey, Piscataway, New Jersey, 08855-0759, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Hilliard
authors.forename: M R
authors.initials: MR
authors.lastname: Maurizi
authors.forename: L D
authors.initials: LD
authors.lastname: Simon
mesh_terms: D049069:ATP-Dependent Proteases; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D017122:Bacteriophage T4 / Q000378:metabolism*; D001704:Biopolymers; D049071:Endopeptidase Clp; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006868:Hydrolysis; D008969:Molecular Sequence Data; D011480:Protease Inhibitors / Q000378:metabolism*; D049070:Protease La; D011485:Protein Binding; D011487:Protein Conformation; D012697:Serine Endopeptidases / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D001704:Biopolymers; C483566:ClpYQ protease, E coli; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; C109919:PinA protein, Enterobacteria phage T4; D011480:Protease Inhibitors; D014764:Viral Proteins; D000255:Adenosine Triphosphate; D049069:ATP-Dependent Proteases; D012697:Serine Endopeptidases; C483567:Lon protein, E coli; D049070:Protease La; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases