RESUMO
Analysis of a crystal structure of alcohol dehydrogenase (Adh) from horse liver suggests that Trp54 in the homologous yeast alcohol dehydrogenase prevents the yeast enzyme from efficiently catalysing the oxidation of long-chain primary alcohols with branching at the 4 position (e.g. 4-methyl-1-pentanol, cinnamyl alcohol). This residue has been altered to Leu by site-directed mutagenesis. The alteration yields an enzyme that serves as an effective catalyst for both longer straight-chain primary alcohols and branched chain alcohols.
Assuntos
Álcool Desidrogenase/metabolismo , Engenharia de Proteínas , Saccharomyces cerevisiae/enzimologia , Álcool Desidrogenase/química , Álcool Desidrogenase/genética , Álcoois/metabolismo , Sítios de Ligação , Cinética , Leucina/química , Mutagênese Sítio-Dirigida , Saccharomyces cerevisiae/genética , Especificidade por Substrato , Triptofano/químicaRESUMO
Replacing Leu-182 by Ala in yeast alcohol dehydrogenase (YADH; alcohol:NAD+ oxidoreductase, EC 1.1.1.1) yields a mutant that retains 34% of its kcat value and makes one stereochemical "mistake" every 850,000 turnovers (instead of approximately 1 error every 7,000,000,000 turnovers in native YADH) in its selection of the 4-Re hydrogen of NADH. Half of the decrease in stereochemical fidelity comes from an increase in the rate of transfer of the 4-Si hydrogen of NADH. The mutant also accepts 5-methylnicotinamide adenine dinucleotide, a cofactor analog not accepted by native YADH. The stereospecificity of the mutant is lower still with analogs of NADH where the carboxamide group of the nicotinamide ring is replaced by groups with weaker hydrogen bonding potential. For example, with thio-NADH, the mutant enzyme makes 1 stereochemical "mistake" every 450 turnovers. Finally, the double mutant T157S/L182A, in which Thr-157 is replaced by Ser and Leu-182 is replaced by Ala, also shows decreased stereochemical fidelity. These results suggest that Si transfer in the mutant enzymes arises from NADH bound in a syn conformation in the active site and that this binding is not obstructed in native YADH by side chains essential for catalysis.
Assuntos
Álcool Desidrogenase/metabolismo , Saccharomyces cerevisiae/enzimologia , Análise Mutacional de DNA , Etanol/metabolismo , Cinética , NAD/metabolismo , Estereoisomerismo , Relação Estrutura-Atividade , Especificidade por SubstratoRESUMO
Paleomolecular biochemistry is a new field of science that seeks to understand how life emerged and developed in interaction with its geophysical surroundings. It is an experimental science, involving reconstruction of extinct biomolecules in the laboratory, studying their properties in the laboratory, and inferring details of their behavior and function in the context of geological data. An outline is provided of some tools of this field, together with its application to the study of two specific systems, ribonuclease and alcohol dehydrogenase.