RESUMO
Structure activity relationship (SAR) investigation of an oxadiazole based series led to the discovery of several potent FLAP inhibitors. Lead optimization focused on achieving functional activity while improving physiochemical properties and reducing hERG inhibition. Several compounds with favorable in vitro and in vivo properties were identified that were suitable for advanced profiling.
Assuntos
Inibidores da Proteína Ativadora de 5-Lipoxigenase/química , Proteínas Ativadoras de 5-Lipoxigenase/metabolismo , Oxidiazóis/química , Inibidores da Proteína Ativadora de 5-Lipoxigenase/metabolismo , Proteínas Ativadoras de 5-Lipoxigenase/química , Animais , Avaliação Pré-Clínica de Medicamentos , Canal de Potássio ERG1/antagonistas & inibidores , Canal de Potássio ERG1/metabolismo , Meia-Vida , Humanos , Concentração Inibidora 50 , Masculino , Microssomos Hepáticos/metabolismo , Oxidiazóis/metabolismo , Ratos , Ratos Sprague-Dawley , Ratos Wistar , Solubilidade , Relação Estrutura-AtividadeRESUMO
Lipoic acid is a sulfur-containing 8-carbon fatty acid that functions as a central cofactor in multienzyme complexes that are involved in the oxidative decarboxylation of glycine and several alpha-keto acids. In its functional form, it is bound covalently in an amide linkage to the epsilon-amino group of a conserved lysine residue of the "lipoyl bearing subunit," resulting in a long "swinging arm" that shuttles intermediates among the requisite active sites. In Escherichia coli and many other organisms, the lipoyl cofactor can be synthesized endogenously. The 8-carbon fatty-acyl chain is constructed via the type II fatty acid biosynthetic pathway as an appendage to the acyl carrier protein (ACP). Lipoyl(octanoyl)transferase (LipB) transfers the octanoyl chain from ACP to the target lysine acceptor, generating the substrate for lipoyl synthase (LS), which subsequently catalyzes insertion of both sulfur atoms into the C-6 and C-8 positions of the octanoyl chain. In this study, we present a three-step isolation procedure that results in a 14-fold purification of LipB to >95% homogeneity in an overall yield of 25%. We also show that the protein catalyzes the transfer of the octanoyl group from octanoyl-ACP to apo-H protein, which is the lipoyl bearing subunit of the glycine cleavage system. The specific activity of the purified protein is 0.541 U mg(-1), indicating a turnover number of approximately 0.2 s(-1), and the apparent Km values for octanoyl-ACP and apo-H protein are 10.2+/-4.4 and 13.2+/-2.9 microM, respectively.
Assuntos
Aciltransferases/isolamento & purificação , Aciltransferases/metabolismo , Proteínas de Escherichia coli/isolamento & purificação , Proteínas de Escherichia coli/metabolismo , Escherichia coli/enzimologia , Expressão Gênica , Proteína de Transporte de Acila/metabolismo , Aciltransferases/genética , Aminoácido Oxirredutases , Apoproteínas/metabolismo , Proteínas de Transporte , Cromatografia em Gel , Cromatografia Líquida de Alta Pressão , Clonagem Molecular , Eletroforese em Gel de Poliacrilamida , Proteínas de Escherichia coli/genética , Histidina/química , Concentração de Íons de Hidrogênio , Ponto Isoelétrico , Cinética , Modelos Biológicos , Peso Molecular , Complexos Multienzimáticos , Concentração Osmolar , Plasmídeos , Reação em Cadeia da Polimerase , Estrutura Quaternária de Proteína , Espectrometria de Massas por Ionização por Electrospray , TransferasesRESUMO
Exchanging the identity of amino acids at four key locations within the Arabidopsis thaliana oleate desaturase (FAD2) and the Lesquerella fendleri hydroxylase/desaturase (LFAH) was shown to influence partitioning between desaturation and hydroxylation (Broun, P., Shanklin, J., Whittle, E., and Somerville, C. (1998) Science 282, 1315-1317). We report that four analogous substitutions in the FAD2 sequence by their equivalents from the castor oleate hydroxylase result in hydroxy fatty acid accumulation in A. thaliana to the same levels as for the wild-type castor hydroxylase. We also describe the relative contribution of these substitutions, both individually and in combination, by analyzing the products resulting from their expression in A. thaliana and/or Saccharomyces cerevisiae. Yeast expression showed that M324V, a change reachable by a single point mutation, altered the product distribution approximately 49-fold, and that residue 148 is also a predominant determinant of reaction outcome. Comparison of residues at position 148 of FAD2, LFAH, and the Ricinus oleate hydroxylase prompted us to rationally engineer LFAH-N149I, a variant with approximately 1.9-fold increase in hydroxylation specificity compared with that of wild-type LFAH. Control experiments showed that the wild-type Arabidopsis thaliana FAD2 desaturase has inherent, low level, hydroxylation activity. Further, fatty acid desaturases from different kingdoms and with different regiospecificities exhibit similar intrinsic hydroxylase activity, underscoring fundamental mechanistic similarities between desaturation and hydroxylation. For LFAH mutants the hydroxylation:desaturation ratio is 5-9-fold higher for 18-carbon versus 16-carbon substrates, supporting our hypothesis that substrate positioning in the active site plays a key role in the partitioning of catalytic specificity.