ABSTRACT
Milroy disease is an autosomal dominant disorder generally presenting with below the knee lymphedema at birth. It is linked to mutations in the tyrosine kinase domain of the VEGFR3 protein which is encoded in the FLT4 gene. Here we report a case of Milroy disease in a patient with a dominant pattern of inheritance, classical physical findings, and lymphatic system imaging demonstrating lack of tracer transport in the lower limbs. Genetic analysis revealed a novel missense mutation compared to a summary of reported mutations causing Milroy Disease.
Subject(s)
Lymphedema/genetics , Mutation, Missense , Vascular Endothelial Growth Factor Receptor-3/genetics , Adolescent , DNA Mutational Analysis , Genetic Predisposition to Disease , Heredity , Humans , Lymphedema/diagnostic imaging , Lymphoscintigraphy , Male , Pedigree , PhenotypeABSTRACT
Leukotriene A(4) hydrolase in mammals is a bifunctional zinc metalloenzyme that catalyzes the hydrolysis of leukotriene A(4) into the proinflammatory mediator leukotriene B(4), and also possesses an aminopeptidase activity. Recently we cloned and characterized an leukotriene A(4) hydrolase from Saccharomyces cerevisiae as a leucyl aminopeptidase with an epoxide hydrolase activity. Here we show that S. cerevisiae leukotriene A(4) hydrolase is a metalloenzyme containing one zinc atom complexed to His-340, His-344, and Glu-363. Mutagenetic analysis indicates that the aminopeptidase activity follows a general base mechanism with Glu-341 and Tyr-429 as the base and proton donor, respectively. Furthermore, the yeast enzyme hydrolyzes leukotriene A(4) into three compounds, viz., 5S,6S-dihydroxy-7,9-trans-11,14-cis-eicosatetraenoic acid, leukotriene B(4), and Delta(6)-trans-Delta(8)-cis-leukotriene B(4), with a relative formation of 1:0.2:0.1. In addition, exposure of S. cerevisiae leukotriene A(4) hydrolase to leukotriene A(4) selectively inactivates the epoxide hydrolase activity with a simultaneous stimulation of the aminopeptidase activity. Moreover, kinetic analyses of wild-type and mutated S. cerevisiae leukotriene A(4) hydrolase suggest that leukotriene A(4) binds in one catalytic mode and one tight-binding, regulatory mode. Exchange of a Phe-424 in S. cerevisiae leukotriene A(4) hydrolase for a Tyr, the corresponding residue in human leukotriene A(4) hydrolase, results in a protein that converts leukotriene A(4) into leukotriene B(4) with an improved efficiency and specificity. Hence, by a single point mutation, we could make the active site better suited to bind and turn over the substrate leukotriene A(4), thus mimicking a distinct step in the molecular evolution of S. cerevisiae leukotriene A(4) hydrolase toward its mammalian counterparts.
Subject(s)
Catalytic Domain , Epoxide Hydrolases/metabolism , Leukotriene B4/biosynthesis , Saccharomyces cerevisiae/enzymology , Amino Acid Sequence , Animals , Binding Sites/genetics , Catalytic Domain/genetics , Enzyme Inhibitors/chemistry , Epoxide Hydrolases/antagonists & inhibitors , Epoxide Hydrolases/biosynthesis , Epoxide Hydrolases/genetics , Escherichia coli/enzymology , Escherichia coli/genetics , Glutamic Acid/genetics , Humans , Hydrolysis , Leukotriene A4/chemistry , Leukotriene A4/metabolism , Leukotriene B4/metabolism , Leukotrienes/metabolism , Molecular Sequence Data , Mutagenesis, Site-Directed , Phenylalanine/genetics , Recombinant Proteins/antagonists & inhibitors , Recombinant Proteins/biosynthesis , Recombinant Proteins/chemistry , Recombinant Proteins/isolation & purification , Spodoptera/enzymology , Spodoptera/genetics , Tyrosine/genetics , Zinc/analysis , Zinc/metabolismABSTRACT
In mammals, leukotriene A(4) hydrolase is a bifunctional zinc metalloenzyme that catalyzes hydrolysis of leukotriene A(4) into the proinflammatory leukotriene B(4) and also possesses an arginyl aminopeptidase activity. We have cloned, expressed, and characterized a protein from Saccharomyces cerevisiae that is 42% identical to human leukotriene A(4) hydrolase. The purified protein is an anion-activated leucyl aminopeptidase, as assessed by p-nitroanilide substrates, and does not hydrolyze leukotriene A(4) into detectable amounts of leukotriene B(4). However, the S. cerevisiae enzyme can utilize leukotriene A(4) as substrate to produce a compound identified as 5S,6S-dihydroxy-7,9-trans-11, 14-cis-eicosatetraenoic acid. Both catalytic activities are inhibited by 3-(4-benzyloxyphenyl)-2-(R)-amino-1-propanethiol (thioamine), a competitive inhibitor of human leukotriene A(4) hydrolase. Furthermore, the peptide cleaving activity of the S. cerevisiae enzyme was stimulated approximately 10-fold by leukotriene A(4) with kinetics indicating the presence of a lipid binding site. Nonenzymatic hydrolysis products of leukotriene A(4), leukotriene B(4), arachidonic acid, or phosphatidylcholine were without effect. Moreover, leukotriene A(4) could displace the inhibitor thioamine and restore maximal aminopeptidase activity, indicating that the leukotriene A(4) binding site is located at the active center of the enzyme. Hence, the S. cerevisiae leukotriene A(4) hydrolase is a bifunctional enzyme and appears to be an early ancestor to mammalian leukotriene A(4) hydrolases.
