title: Endonuclease activity in lipocalins.
abstract: Several lipocalins contain conserved amino acid sequences similar to the phosphodiester bond cleavage domain of sugar non-specific magnesium-dependent nucleases of the Serratia marcescens type. His-89 and Glu-127 of the S. marcescens endonuclease are believed to have a role in the active catalytic site by the attack of a water molecule at the phosphorus atom of the bridging phosphate. Tear lipocalin contains both amino acids in analogous regions, and is active as a nuclease. Two forms of beta-lactoglobulin contain only Glu-134 (analogous to Glu-127 of the Serratia nuclease) yet retain nuclease activity equal to or greater than that of tear lipocalin. However, retinol-binding protein lacks both of these motifs and shows no detectable activity. DNA-nicking activity is decreased by 80% in the mutant of tear lipocalin that replaces Glu-128 but is unchanged by mutations of His-84. The endonuclease activity of tear lipocalin is dependent on the bivalent cations Mg(2+) or Mn(2+) but is decreased at high concentrations of NaCl. These findings indicate that some lipocalins have non-specific endonuclease activity similar in characteristics to the Mg(2+)-dependent nucleases and related to the conserved sequence LEDFXR (where 'X' denotes 'any other residue'), in which the glutamic residue seems to be important for activity.
authors.affiliation: Departments of Pathology and Ophthalmology, University of California, Los Angeles, School of Medicine, Los Angeles, CA 90095, USA.
authors.forename: T N
authors.initials: TN
authors.lastname: Yusifov
authors.forename: A R
authors.initials: AR
authors.lastname: Abduragimov
authors.forename: O K
authors.initials: OK
authors.lastname: Gasymov
authors.forename: B J
authors.initials: BJ
authors.lastname: Glasgow
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D002417:Cattle; D002942:Circular Dichroism; D017124:Conserved Sequence / Q000235:genetics; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004720:Endonucleases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D007782:Lactoglobulins / Q000737:chemistry / Q000378:metabolism*; D054835:Lipocalin 1; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D012177:Retinol-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D012706:Serratia marcescens / Q000201:enzymology*
chemical_list: D002352:Carrier Proteins; D002413:Cations, Divalent; C518443:LCN1 protein, human; D007782:Lactoglobulins; D054835:Lipocalin 1; D012177:Retinol-Binding Proteins; D018698:Glutamic Acid; D006639:Histidine; D004247:DNA; D004720:Endonucleases