title: Mutagenesis and kinetic studies of a plant cysteine proteinase with an unusual arrangement of acidic amino acids in and around the active site.
abstract: We report the cloning, overexpression, kinetic analysis, and modeling of the tertiary structure of an unusual plant cysteine proteinase. Ananain (EC 3.4.22.31), from Ananas comosus (pineapple) is distinguished from all other cysteine proteinases in the papain superfamily by having a unique combination of acidic amino acids. As well as lacking the acidic residue immediately preceding the active site histidine (position 158 in papain), it also lacks the extensive surface network of acidic residues that were postulated to compensate for the loss of charge at position 158 in mammalian cathepsins. Ananain has the fewest acidic residues, so far reported, of any plant cysteine proteinase, but two of the carboxyl residues (E50 and E35) postulated to have an enabling role in catalysis, the so-called "electrostatic switch", remain conserved. Comparisons of the kinetics of recombinant wild-type ananain with E50A and E35A mutants proves that these charged groups are not essential for catalysis. Hence this research does not confirm the presence of an electrostatic switch in this cysteine proteinase, and the role of acidic residues in the enhancement of catalytic competence in these enzymes is discussed in light of this new evidence.
authors.affiliation: Wolfson Protein Engineering Facility, School of Plant Sciences, Plant Science Laboratories, University of Reading, Whiteknights, P.O. Box 221, Reading RG6 6AS, U.K.
authors.forename: C E
authors.initials: CE
authors.lastname: Carter
authors.forename: H
authors.initials: H
authors.lastname: Marriage
authors.forename: P W
authors.initials: PW
authors.lastname: Goodenough
mesh_terms: D000409:Alanine / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001216:Asparagine / Q000235:genetics / Q000378:metabolism; D001224:Aspartic Acid / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000302:isolation & purification; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019684:Magnoliopsida; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D011498:Protein Precursors / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
chemical_list: D018076:DNA, Complementary; D010940:Plant Proteins; D011498:Protein Precursors; D011994:Recombinant Proteins; D001224:Aspartic Acid; D018698:Glutamic Acid; D001216:Asparagine; D003546:Cysteine Endopeptidases; C057808:ananain; D000409:Alanine