1sqm
From Proteopedia
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STRUCTURE OF [R563A] LEUKOTRIENE A4 HYDROLASE
Overview
Leukotriene (LT) A(4) hydrolase is a bifunctional zinc metalloenzyme, which converts LTA(4) into the neutrophil chemoattractant LTB(4) and also, exhibits an anion-dependent aminopeptidase activity. In the x-ray crystal, structure of LTA(4) hydrolase, Arg(563) and Lys(565) are found at the, entrance of the active center. Here we report that replacement of, Arg(563), but not Lys(565), leads to complete abrogation of the epoxide, hydrolase activity. However, mutations of Arg(563) do not seem to affect, substrate binding strength, because values of K(i) for LTA(4) are almost, identical for wild type and (R563K)LTA(4) hydrolase. These results are, supported by the 2.3-A crystal structure of (R563A)LTA(4) hydrolase, which, does not reveal structural changes that can explain the complete loss of, enzyme function. For the aminopeptidase reaction, mutations of Arg(563), reduce the catalytic activity (V(max) = 0.3-20%), whereas mutations of, Lys(565) have limited effect on catalysis (V(max) = 58-108%). However, in, (K565A)- and (K565M)LTA(4) hydrolase, i.e. mutants lacking a positive, charge, values of the Michaelis constant for alanine-p-nitroanilide, increase significantly (K(m) = 480-640%). Together, our data indicate that, Arg(563) plays an unexpected, critical role in the epoxide hydrolase, reaction, presumably in the positioning of the carboxylate tail to ensure, perfect substrate alignment along the catalytic elements of the active, site. In the aminopeptidase reaction, Arg(563) and Lys(565) seem to, cooperate to provide sufficient binding strength and productive alignment, of the substrate. In conclusion, Arg(563) and Lys(565) possess distinct, roles as carboxylate recognition sites for two chemically different, substrates, each of which is turned over in separate enzymatic reactions, catalyzed by LTA(4) hydrolase.
About this Structure
1SQM is a Single protein structure of sequence from Homo sapiens with ZN, YB, IMD and ACY as ligands. Active as Leukotriene-A(4) hydrolase, with EC number 3.3.2.6 Full crystallographic information is available from OCA.
Reference
Leukotriene A4 hydrolase: identification of a common carboxylate recognition site for the epoxide hydrolase and aminopeptidase substrates., Rudberg PC, Tholander F, Andberg M, Thunnissen MM, Haeggstrom JZ, J Biol Chem. 2004 Jun 25;279(26):27376-82. Epub 2004 Apr 12. PMID:15078870
Page seeded by OCA on Mon Nov 12 19:16:51 2007
