Evaluation of the role of conserved His and Met residues among lipoxygenases by site-directed mutagenesis of recombinant human 5-lipoxygenase.
The 5-, 12-, and 15-lipoxygenases contain a highly conserved sequence of the form His-(X)4-His-(X)4-His-(X)17-His-(X)8-His which represents a potential binding site for non heme iron to the protein. The importance of selected amino acids within this His cluster for the activity of human 5-lipoxygenase was investigated by site-directed mutagenesis using bacteria and insect cells expression systems. After single mutation of each of the 5 His residues at positions 363, 368, 373, 391, and 400 by Ser, Cys, or Lys, measurable levels of 5-lipoxygenase activity could be recovered in Escherichia coli only for the Ser363 and Cys363 mutants, with most amino acid substitutions causing a decrease in the levels of expression of the soluble protein. In contrast, 25-80% of soluble 5-lipoxygenase activity was recovered after the replacement of several of the hydrophobic amino acids in this region: Tyr384 by Ser or Phe; Phe394 by Trp and Val375 by Ala. Met436 could be replaced by Leu with little effect on 5-lipoxygenase activity or turnover inactivation half-time. High levels of mutant 5-lipoxygenases containing a Ser residue instead of His at each of the five positions were also expressed in Spodoptera frugiperda (Sf9) cells infected with recombinant baculovirus. The specific activity (58-75% of control) and the reaction time course of the Ser363, Ser391, and Ser400 mutants were comparable with that of native 5-lipoxygenase whereas inactive proteins were obtained for the Ser368 and Ser373 mutants. These results show that His368 and His373 residues are important for 5-lipoxygenase activity and that the other conserved His363, His391, His400, and Met436 residues are not crucial for the catalytic cycle or for the mechanism of self-inactivation of 5-lipoxygenase.
Nguyen
T
T
Department of Molecular Biology, Merck Frosst Centre for Therapeutic Research, Kirkland, Québec, Canada.
Falgueyret
J P
JP
Abramovitz
M
M
Riendeau
D
D
D000595:Amino Acid Sequence; D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000235:genetics* / Q000378:metabolism; D016367:Baculoviridae; D005075:Biological Evolution; D002460:Cell Line; D003001:Cloning, Molecular; D005822:Genetic Vectors; D006639:Histidine; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D008084:Lipoxygenase / Q000235:genetics* / Q000378:metabolism; D008715:Methionine; D008969:Molecular Sequence Data; D009036:Moths; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection
D011994:Recombinant Proteins; D006639:Histidine; D008715:Methionine; D008084:Lipoxygenase; D001094:Arachidonate 5-Lipoxygenase