Purification and molecular characterization of alcohol dehydrogenase from Drosophila hydei: conservation in the biochemical features of the enzyme in several species of Drosophila

Drosophila alcohol dehydrogenase: acetate-enzyme interactions and novel insights into the effects of electrostatics on catalysis

Drosophila alcohol dehydrogenase (DADH) is an NAD+-dependent enzyme that catalyzes the oxidation of alcohols to aldehydes/ketones and that is also able to further oxidize aldehydes to their corresponding carboxylic acids. The structure of the ternary enzyme-NADH-acetate complex of the slow alleloform of Drosophila melanogaster ADH (DmADH-S) was solved at 1.6 A resolution by X-ray crystallography. The coenzyme stereochemistry of the aldehyde dismutation reaction showed that the obtained enzyme-NADH-acetate complex reflects a productive ternary complex although no enzymatic reaction occurs. The stereochemistry of the acetate binding in the bifurcated substrate-binding site, along with previous stereochemical studies of aldehyde reduction and alcohol oxidation shows that the methyl group of the aldehyde in the reduction reaction binds to the R1 and in the oxidation reaction to the R2 sub-site. NMR studies along with previous kinetic studies show that the formed acetaldehyde intermediate in the oxidation of ethanol to acetate leaves the substrate site prior to the reduced coenzyme, and then binds to the newly formed enzyme-NAD+ complex. Here, we compare the three-dimensional structure of D.melanogaster ADH-S and a previous theoretically built model, evaluate the differences with the crystal structures of five Drosophila lebanonensis ADHs in numerous complexed forms that explain the substrate specificity as well as subtle kinetic differences between these two enzymes based on their crystal structures. We also re-examine the electrostatic influence of charged residues on the surface of the protein on the catalytic efficiency of the enzyme.

Isolation and partial characterization of two alcohol dehydrogenase isozymes from the medfly Ceratitis capitata

Two alcohol dehydrogenase isozymes, namely ADH-1 and ADH-2 from Ceratitis capitata were purified to homogeneity and further characterized. After ammonium sulphate precipitation from an extract of whole third instar larvae, the two isozymes were separated by ion exchange chromatography on Q-Sepharose. A combination of affinity chromatography, gel filtration and ion exchange chromatography was then used to purify each isozyme (50 and 57 times with 53 and 58% yields, for ADH-1 and -2 respectively). A crucial step for obtaining homogeneous enzyme preparations was affinity chromatography on Cibacron Blue Sepharose coupled with specific elution with NAD. Each of the isozymes is a dimer with subunit molecular weight of approximately 27 kDa. Both isozymes show a pH optimum of 9.6. ADH-1 proved to be immunochemically similar to ADH-2 when tested by Western blot analysis using polyclonal antibodies raised against ADH-1. While crude extracts of Dacus oleae ADH cross-react with these antibodies, no cross reactivity was observed with Drosophila melanogaster extracts. The sequence of a 22-residue peptide from ADH-1 was determined and showed 36% identity with residues 26-47 of the Drosophila melanogaster ADH sequence. Both the sizes of the purified proteins and the observed sequence similarity between ADH-1 and Drosophila ADH strongly suggest that the medfly ADH isozymes belong to the family of short chain dehydrogenases.

Evidence of serine-protease activity closely associated with Drosophila alcohol dehydrogenase

With the use of monoclonal antibodies against alcohol dehydrogenase (ADH) we detected ADH proteolysis in different Drosophila melanogaster tissues during development [Visa, N., Fiblas, J., Santa-Crus, M. C. & Gonzàlez-Duarte R. (1992) J. Histochem. Cytochem. 40, 39-49]. We now report the analysis of this proteolytic activity in crude homogenates and in purified ADH preparations of several Drosophila species. Our results indicate that in non-denaturing IEF gels the proteolytic activity comigrates with native ADH electromorphs of all the species analyzed. In addition, we show that it copurifies with ADH and is responsible for the instability of apparently homogeneous ADH preparations in the presence of SDS. When purified ADH preparations were analyzed, the endogenous proteolytic activity yielded the same banding pattern as that obtained with crude homogenates. Even after rechromatography on Sephacryl S-200, the usual last step in our standard purification protocol, the proteolytic activity remained associated with the ADH fractions. Among the various agents which could explain the ADH-linked proteolytic effect, a pre-existing nicked state of the enzyme or chemical proteolysis have been ruled out. The kinetics observed on pure ADH preparations, the effect of specific protease inhibitors and substrate specificity have led us to ascribe this activity to the subtilase serine-protease family. Given that proteolysis is evident even in rechromatographed Sephacryl S-200 fractions, if incubated in SDS for enough time, we propose two alternative hypotheses to explain this phenomenon. First, the proteolytic activity may come from a protease which is inseparable from the ADH active forms and second, the ADH itself may behave as a subtilase when it adopts a particular conformation. Moreover, the previously reported differential banding pattern during development suggests a role for this activity in vivo, in which fatty acids could produce the inducer effect attributed to SDS in vitro.

A biochemical genetic study of alcohol dehydrogenase isozymes of the medfly, Ceratitis capitata Wied

A concerted effort is under way to analyze, at the genetic, biochemical, and molecular level, the Adh gene system in the medfly Ceratitis capitata, an important agricultural pest. The isoelectric focusing (IEF) pattern of alcohol dehydrogenase (ADH) of the medfly demonstrates the presence of two well-differentiated, genetically independent dimeric proteins, called ADH-1 and ADH-2. These proteins do not exhibit interlocus heterodimeric isozymes, and the genes are not controlled coordinately during development, Adh1 and Adh2 being expressed mainly in muscle or in fat body and ovary, respectively. From the intensity of the IEF isozyme patterns, primary alcohols are judged to be better substrates than secondary alcohols, in contrast with Drosophila melanogaster ADH, and ethanol is probably the most efficient substrate for both sets of isozymes. The isoelectric points of ADH-1 (pI = 5.4) and ADH-2 (pI = 8.6) are different from D. melanogaster ADH (pI = 7.6), but the medfly ADH-1 has a native molecular weight (approx. 58 kD) close to that of D. melanogaster. A population survey of samples both from laboratory strains and from wild geographically different populations showed that the Adh1 locus is more polymorphic than Adh2. The most variable populations are from Africa, the supposed source area of the species. Further, a case of selection at the Adh1 locus under laboratory conditions is reported. The hypothesis of Adh gene duplication and the degree of similarity between medfly and Drosophila ADH are also discussed.

Kinetic interpretations of active site topologies and residue exchanges in Drosophila alcohol dehydrogenases

1. A comparison of full and partly sequenced Adhs from various Drosophila species reveal that 127 of their 253-255 positions are identical (50% identity). 2. Fifty-six of the 115 C-terminal amino acids building up the alcohol binding region differ. In spite of the large differences in primary structure of the alcohol binding region in the Adh enzyme in distantly related Drosophila species, the substrate specificity and stereospecificity have been retained. The topology of the alcohol binding region has been largely conserved during evolution. 3. The primary structures of the alcohol dehydrogenases (Adh) in the Sophophora subgenus is distinguished by few amino acid exchanges, and kinetic and activity parameters show that those at positions 14, 82, 192 and 214 are directly or indirectly involved in coenzyme binding. 4. In these non-metallo Adhs, a tyrosine has been tentatively identified as a nucleophilic catalyst of the hydride transfer step. The three tyrosines at positions 63, 152 and 178 are conserved among the Drosophila alcohol dehydrogenases.

Isolation of a cDNA encoding functional Drosophila alcohol dehydrogenase in Escherichia coli and purification of the bacterially produced enzyme

Because of the severe limitations on growing large quantities of Drosophila affinidisjuncta in the laboratory, direct purification of alcohol dehydrogenase (ADH) from this species has proven impossible. As an alternative source of this enzyme, a cDNA encoding functional ADH was isolated from a newly constructed cDNA library made from larval poly(A)-containing RNA. The cDNA was recovered by virtue of its hybridization to a previously isolated genomic ADH gene. Nucleotide sequence analysis confirmed the identity of the newly isolated cDNA. When the cDNA was inserted in the proper orientation downstream of the lac promoter on the vector pUC8, the cDNA directed the synthesis of functional ADH by the bacterial host. The bacterially produced enzyme was purified to homogeneity and used to elicit polyclonal antibodies in rabbits. The purified ADH has identical apparent subunit molecular weight to that of authentic ADH in larval fly extracts as determined by immunoblotting. Further, comparisons of the kinetic parameters of the bacterially produced enzyme and ADH activity in larval fly extracts indicate similar substrate preferences, pH dependencies, and Km values for 2-propanol and NAD. These results show that expression of a cDNA in Escherichia coli is a valid strategy for isolation of an ADH that would otherwise be difficult or impossible to purify.

Inter-specific analysis of Drosophila alcohol dehydrogenase by an immunoenzymatic assay using monoclonal antibodies

Three Drosophila alcohol dehydrogenase monoclonal antibodies have been prepared and characterized. These antibodies cross-react with alcohol dehydrogenase from different species as revealed by immunoblotting assay. An enzyme-linked immunosorbent assay has been devised to quantify alcohol dehydrogenase in several species, different strains and individual larval organs. The assay detects alcohol dehydrogenase via a double-antibody sandwich assay technique giving strictly proportional values for antigen concentration and optical densities in the range of 3-30 ng of antigen per 100 microliters of sample. When alcohol dehydrogenase specific activity is compared in different larval organs a remarkable similarity is observed, whereas protein distribution varies substantially. Larval fat body and larval alimentary canal contribute 63% and 26% respectively to recovered alcohol dehydrogenase.

Functional and biochemical features of alcohol dehydrogenase in four species of the obscura group of Drosophila

The biochemical features of ADH of four Drosophila species of the obscura group have been studied. The relationship between ethanol tolerance and ADH activity has been investigated. Propan-2-ol and acetone concentrations have been determined in propan-2-ol treated flies and ADH activity has been followed during 96 h of propan-2-ol treatment. Data on the ADH system confirm constructed phylogenies based on electrophoretic variation and chromosome homologies.