title: The structure of bacteriophage T7 lysozyme, a zinc amidase and an inhibitor of T7 RNA polymerase.
abstract: The lysozyme of bacteriophage T7 is a bifunctional protein that cuts amide bonds in the bacterial cell wall and binds to and inhibits transcription by T7 RNA polymerase. The structure of a mutant T7 lysozyme has been determined by x-ray crystallography and refined at 2.2-A resolution. The protein folds into an alpha/beta-sheet structure that has a prominent cleft. A zinc atom is located in the cleft, bound directly to three amino acids and, through a water molecule, to a fourth. Zinc is required for amidase activity but not for inhibition of T7 RNA polymerase. Alignment of the zinc ligands of T7 lysozyme with those of carboxypeptidase A and thermolysin suggests structural similarity among the catalytic sites for the amidase and these zinc proteases. Mutational analysis identified presumed catalytic residues for amidase activity within the cleft and a surface that appears to be the site of binding to T7 RNA polymerase. Binding of T7 RNA polymerase inhibits amidase activity.
authors.affiliation: W. M. Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, NY 11724.
authors.forename: X
authors.initials: X
authors.lastname: Cheng
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: J W
authors.initials: JW
authors.lastname: Pflugrath
authors.forename: F W
authors.initials: FW
authors.lastname: Studier
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism / Q000648:ultrastructure*; D000595:Amino Acid Sequence; D017123:Bacteriophage T7 / Q000201:enzymology*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors*; D008667:Metalloproteins / Q000648:ultrastructure; D008969:Molecular Sequence Data; D009113:Muramidase / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D014764:Viral Proteins; D015032:Zinc
chemical_list: D008667:Metalloproteins; D014764:Viral Proteins; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases; D009113:Muramidase; D000581:Amidohydrolases; D015032:Zinc