Leukotriene A4 Hydrolase/Aminopeptidase, Glutamate 271 is a Catalyticresidue with Specific Roles in Two Distinct Enzyme MechanismsRudberg, P.C., Tholander, F., Thunnissen, M.M.G.M., Haeggstrom, J.Z.
(2002) J Biol Chem 277: 1398
- PubMed: 11675384
- DOI: 10.1074/jbc.M106577200
- Primary Citation of Related Structures:
- PubMed Abstract:
Leukotriene A(4) hydrolase/aminopeptidase is a bifunctional zinc metalloenzyme that converts the fatty acid epoxide leukotriene A(4) into leukotriene B(4), a potent chemoattractant and immune-modulating lipid mediator. Recently, the structure of leukotri ...
Leukotriene A(4) hydrolase/aminopeptidase is a bifunctional zinc metalloenzyme that converts the fatty acid epoxide leukotriene A(4) into leukotriene B(4), a potent chemoattractant and immune-modulating lipid mediator. Recently, the structure of leukotriene A(4) hydrolase revealed that Glu-271, which belongs to a conserved GXMEN motif in the M1 family of zinc peptidases, and Gln-136 are located at the active site. Here we report that mutagenetic replacements of Glu-271, but not Gln-136, abrogate both catalytic activities of leukotriene A(4) hydrolase. Furthermore, the 2.1 A crystal structure of [E271Q]leukotriene A(4) hydrolase revealed minimal conformational changes that could not explain the loss of enzyme function. We propose that the carboxylate of Glu-271 participates in an acid-induced opening of the epoxide moiety of leukotriene A(4) and formation of a carbocation intermediate. Moreover, Glu-271 appears to act as an N-terminal recognition site and may potentially stabilize the transition-state during turnover of peptides, a property that most likely pertains to all members of the M1 family of zinc aminopeptidases. Hence, Glu-271 is a unique example of an amino acid, which has dual and separate functions in two different catalytic reactions, involving lipid and peptide substrates, respectively.
Department of Medical Biochemistry and Biophysics, Division of Chemistry II, Karolinska Institutet, S-171 77 Stockholm, Sweden.