Structural characterization of the covalent attachment of leukotriene A3 to leukotriene A4 hydrolase.
Leukotriene A4 (LTA4) hydrolase catalyzes the conversion of the unstable epoxide LTA4 [5(S)-trans-5,6-oxido-11,14-cis-eicosatetraenoic acid] into proinflammatory LTB4. During the process of catalyzing this reaction, the enzyme is suicide inactivated by its substrate. In addition, LTA3, and analogue of LTA4 that lacks the C14-C15 double bond, is a potent suicide inhibitor of LTA4 hydrolase. We have synthesized [3H]LTA3 and used this ligand to demonstrate that LTA3 can covalently label LTA4 hydrolase and that this labeling is specifically competed for by bestatin and LTA4. Incubation of recombinant human LTA4 hydrolase with LTA3 followed by proteolysis (endoproteinase Lys-C) resulted in a peptide map with a single modified peptide defining the location of the LTA3 covalent attachment region. This modified 21-amino-acid peptide had a UV absorption spectrum corresponding to a conjugated triene chromophore which established conservation of this structural unit after covalent interaction of LTA3 with LTA4 hydrolase. MALDI-TOF mass spectrometric analysis of the 21-amino-acid peptide adduct revealed an abundant MH+ at m/z 2658, consistent with the predicted nominal mass of the sequenced peptide with the addition of a single LTA3 moiety. Proteolysis of LTA4 hydrolase modified with LTA3 was performed sequentially with endo-Asp-N and endo-Lys-C. The resulting peptide isolated by reverse-phase high-performance liquid chromatography was analyzed by mass spectroscopy revealing two related peptides, D371-K385 (m/z 2018.0) and D375-K385 (m/z 1577.8), both of which retained the elements of LTA3. Postsource decay of m/z 1577.8 resulted in an abundant ion at m/z 536 and an ion of lesser abundance at m/z 856 consistent with cleavage between V381 and P382 that supported assignment of the modified tyrosine residue at Y383. These results suggest nucleophilic attack of a tyrosine residue (Y383) at the conjugated triene epoxide of LTA3 resulting in a triene ether carbinol covalent adduct.
Mancini
J A
JA
Department of Biochemistry, McGill University, Montreal, PQ, Canada.
Waugh
R J
RJ
Thompson
J A
JA
Evans
J F
JF
Belley
M
M
Zamboni
R
R
Murphy
R C
RC
D000595:Amino Acid Sequence; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D004851:Epoxide Hydrolases / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D017572:Leukotriene A4 / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010455:Peptides / Q000302:isolation & purification / Q000378:metabolism; D013379:Substrate Specificity; D014316:Tritium
C109469:14,15-dehydroleukotriene A4; D017572:Leukotriene A4; D010455:Peptides; D014316:Tritium; D004851:Epoxide Hydrolases; C043134:leukotriene A4 hydrolase