RESUMO
1-Aminocyclopropane carboxylic acid oxidase (ACCO) catalyzes the last step of ethylene biosynthesis in plants. Although some sets of structures have been described, there are remaining questions on the active conformation of ACCO and in particular, on the conformation and potential flexibility of the C-terminal part of the enzyme. Several techniques based on the introduction of a probe through chemical modification of amino acid residues have been developed for determining the conformation and dynamics of proteins. Cysteine residues are recognized as convenient targets for selective chemical modification of proteins, thanks to their relatively low abundance in protein sequences and to their well-mastered chemical reactivity. ACCOs have generally 3 or 4 cysteine residues in their sequences. By a combination of approaches including directed mutagenesis, activity screening on cell extracts, biophysical and biochemical characterization of purified enzymes, we evaluated the effect of native cysteine replacement and that of insertion of cysteines on the C-terminal part in tomato ACCO. Moreover, we have chosen to use paramagnetic labels targeting cysteine residues to monitor potential conformational changes by electron paramagnetic resonance (EPR). Given the level of conservation of the cysteines in ACCO from different plants, this work provides an essential basis for the use of cysteine as probe-anchoring residues.
Assuntos
Aminoácido Oxirredutases/química , Aminoácidos Cíclicos/química , Cisteína/química , Etilenos/química , Óxidos de Nitrogênio/química , Proteínas de Plantas/química , Solanum lycopersicum/enzimologia , Aminoácido Oxirredutases/genética , Aminoácido Oxirredutases/metabolismo , Substituição de Aminoácidos , Aminoácidos Cíclicos/metabolismo , Sítios de Ligação , Clonagem Molecular , Cisteína/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Escherichia coli/genética , Escherichia coli/metabolismo , Etilenos/biossíntese , Expressão Gênica , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Cinética , Solanum lycopersicum/química , Modelos Moleculares , Mutagênese Sítio-Dirigida , Óxidos de Nitrogênio/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Marcadores de Spin , Especificidade por SubstratoRESUMO
Ethylene is a key molecule in organic synthesis currently produced by steam cracking of fossil hydrocarbons. In nature, ethylene is produced in higher plants by 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO). Biocatalytic alternatives for ethylene production are still far from being competitive with traditional production plants. Furthermore, data dispersion shown in the literature adds uncertainty to the introduction of ACCO as a biocatalyst, especially when larger numbers of isoforms or mutants are to be compared. Here we propose a new method for measuring ACCO activity based on cyanide detection. Data provided here indicate that cyanide detection is more precise, more responsive, and much more stable than any other method tested for ACCO activity estimation so far. Briefly, enzymatically produced cyanide can be detected by its derivatization with naphthalene-2,3-dicarboxyaldehide (NDA) to generate 1-cyanobenz[f]isoindole (CBI), which is further detected by high-performance liquid chromatography (HPLC) coupled with a fluorescence detector. Cyanide can be detected in the range between 0.99 and 60.17pmol, which is three orders of magnitude more sensitive than the currently used ethylene estimation method.