Changes in Protein Patterns of Pea Plants Systemically Infected with Red Clover Mottle Virus

Pseudomonad cyclopentadecanone monooxygenase displaying an uncommon spectrum of Baeyer-Villiger oxidations of cyclic ketones

Baeyer-Villiger monooxygenases (BVMOs) are biocatalysts that offer the prospect of high chemo-, regio-, and enantioselectivity in the organic synthesis of lactones or esters from a variety of ketones. In this study, we have cloned, sequenced, and overexpressed in Escherichia coli a new BVMO, cyclopentadecanone monooxygenase (CpdB or CPDMO), originally derived from Pseudomonas sp. strain HI-70. The 601-residue primary structure of CpdB revealed only 29% to 50% sequence identity to those of known BVMOs. A new sequence motif, characterized by a cluster of charged residues, was identified in a subset of BVMO sequences that contain an N-terminal extension of approximately 60 to 147 amino acids. The 64-kDa CPDMO enzyme was purified to apparent homogeneity, providing a specific activity of 3.94 micromol/min/mg protein and a 20% yield. CPDMO is monomeric and NADPH dependent and contains approximately 1 mol flavin adenine dinucleotide per mole of protein. A deletion mutant suggested the importance of the N-terminal 54 amino acids to CPDMO activity. In addition, a Ser261Ala substitution in a Rossmann fold motif resulted in an improved stability and increased affinity of the enzyme towards NADPH compared to the wild-type enzyme (K(m) = 8 microM versus K(m) = 24 microM). Substrate profiling indicated that CPDMO is unusual among known BVMOs in being able to accommodate and oxidize both large and small ring substrates that include C(11) to C(15) ketones, methyl-substituted C(5) and C(6) ketones, and bicyclic ketones, such as decalone and beta-tetralone. CPDMO has the highest affinity (K(m) = 5.8 microM) and the highest catalytic efficiency (k(cat)/K(m) ratio of 7.2 x 10(5) M(-1) s(-1)) toward cyclopentadecanone, hence the Cpd designation. A number of whole-cell biotransformations were carried out, and as a result, CPDMO was found to have an excellent enantioselectivity (E > 200) as well as 99% S-selectivity toward 2-methylcyclohexanone for the production of 7-methyl-2-oxepanone, a potentially valuable chiral building block. Although showing a modest selectivity (E = 5.8), macrolactone formation of 15-hexadecanolide from the kinetic resolution of 2-methylcyclopentadecanone using CPDMO was also demonstrated.

Purification and characterization of the soluble methane monooxygenase of the type II methanotrophic bacterium Methylocystis sp. strain WI 14

Methane monooxygenase (MMO) catalyzes the oxidation of methane to methanol as the first step of methane degradation. A soluble NAD(P)H-dependent methane monooxygenase (sMMO) from the type II methanotrophic bacterium WI 14 was purified to homogeneity. Sequencing of the 16S rDNA and comparison with that of other known methanotrophic bacteria confirmed that strain WI 14 is very close to the genus Methylocystis. The sMMO is expressed only during growth under copper limitation (<0.1 microM) and with ammonium or nitrate ions as the nitrogen source. The enzyme exhibits a low substrate specificity and is able to oxidize several alkanes and alkenes, cyclic hydrocarbons, aromatics, and halogenic aromatics. It has three components, hydroxylase, reductase and protein B, which is involved in enzyme regulation and increases sMMO activity about 10-fold. The relative molecular masses of the native components were estimated to be 229, 41, and 18 kDa, respectively. The hydroxylase contains three subunits with relative molecular masses of 57, 43, and 23 kDa, which are present in stoichiometric amounts, suggesting that the native protein has an alpha(2)beta(2)gamma(2) structure. We detected 3.6 mol of iron per mol of hydroxylase by atomic absorption spectrometry. sMMO is strongly inhibited by Hg(2+) ions (with a total loss of enzyme activity at 0.01 mM Hg(2+)) and Cu(2+), Zn(2+), and Ni(2+) ions (95, 80, and 40% loss of activity at 1 mM ions). The complete sMMO gene sequence has been determined. sMMO genes from strain WI 14 are clustered on the chromosome and show a high degree of homology (at both the nucleotide and amino acid levels) to the corresponding genes from Methylosinus trichosporium OB3b, Methylocystis sp. strain M, and Methylococcus capsulatus (Bath).

Crotonobetaine reductase from Escherichia coli consists of two proteins

Crotonobetaine reductase from Escherichia coli is composed of two proteins (component I (CI) and component II (CII)). CI has been purified to electrophoretic homogeneity from a cell-free extract of E. coli O44 K74. The purified protein shows l(-)-carnitine dehydratase activity and its N-terminal amino acid sequence is identical to the caiB gene product from E. coli O44 K74. The relative molecular mass of CI has been determined to be 86100. It is composed of two identical subunits with a molecular mass of 42600. The isoelectric point of CI was found to be 4.3. CII was purified from an overexpression strain in one step by ion exchange chromatography on Fractogel EMD TMAE 650(S). The N-terminal amino acid sequence of CII shows absolute identity with the N-terminal sequence of the caiA gene product, i.e. of the postulated crotonobetaine reductase. The relative molecular mass of the protein is 164400 and it is composed of four identical subunits of molecular mass 41500. The isoelectric point of CII is 5.6. CII contains non-covalently bound FAD in a molar ratio of 1:1. In the crotonobetaine reductase reaction one dimer of CI associates with one tetramer of CII. A still unknown low-molecular-mass effector described for the l(-)-carnitine dehydratase is also necessary for crotonobetaine reductase activity. Monoclonal antibodies were raised against the two components of crotonobetaine reductase.

Purification and properties of methanol dehydrogenase from Methylocystis sp. GB 25

Methanol dehydrogenase (MDH) from Methylocystis sp. GB 25, which belongs to the group II of methanotrophic bacteria, is able to catalyse the oxidation of methanol to formate directly. The enzyme was purified 20-fold by a 5 step procedure to electrophoretic homogeneity. After cell disruption by French press, about 95% of MDH-activity was found in the soluble fraction. The relative molecular mass of the native enzyme has been estimated to be 122 kDa by gel filtration and 115 kDa by the method of Hedrick and Smith (1968). It seems to be composed of two identical subunits with a relative molecular mass of 62 kDa (estimated by SDS gel electrophoresis). The isoelectric point was found to be about 8.3. The amino terminal sequence shows a strong similarity to the alpha-chain of MDH from the facultative methylotrophic bacterium Methylobacterium extorquens AM1. PQQ, the probable prosthetic group of MDH, could be detected in the supernatant of the culture by using the apoenzyme of a membrane-bound glucose dehydrogenase from Pseudomonas aeruginosa but not absolutely in the absorption spectra of the enzyme after DEAE-chromatography. The purified MDH has an optimum activity at pH 9.0 and at 45 degrees C. MDH of Methylocystis sp. GB 25 oxidises only primary alcohols from methanol to heptanol and aldehydes from formaldehyde to propionaldehyde and the glutaraldehyde, respectively. The estimated Km-values show no dependence upon the chain length of substrates.

Purification and characterization of D(+)-carnitine dehydrogenase from Agrobacterium sp.--a new enzyme of carnitine metabolism

D(+)-Carnitine dehydrogenase from Agrobacterium sp. catalyzes the oxidation of D(+)-carnitine to 3-dehydrocarnitine as initial step of D(+)-carnitine degradation. The NAD(+)-specific, cytosolic enzyme was purified 126-fold to apparent electrophoretic homogeneity by 4 chromatographic steps. The molecular mass of the native enzyme was estimated to be 88 kDa by size-exclusion chromatography. It seems to be composed of 3 identical subunits with a relative molecular mass of 28 kDa as found by sodium dodecyl sulfate polyacrylamide gel electrophoresis and laser-induced mass spectrometry. The isoelectric point was found to be 4.7-5.0. The optimum temperature is 37 degrees C and the optimum pH for the oxidation and the reduction reaction are 9.0-9.5 and 5.5-6.5, respectively. The purified enzyme was further characterized with respect to substrate specificity, kinetic parameters and amino terminal sequence. Analogues of D(+)-carnitine (L(-)-carnitine, crotonobetaine, gamma-butyrobetaine, carnitine amide, glycine betaine, choline) are competitive inhibitors of D(+)-carnitine oxidation. The equilibrium constant of the reaction of D(+)-carnitine dehydrogenase was determined to be 2.2 x 10(-12). The purified D(+)-carnitine dehydrogenase has similar kinetic properties to the L(-)-carnitine dehydrogenase from the same microorganism as well as to L(-)-carnitine dehydrogenases of other bacteria.

Purification and properties of L(-)-carnitine dehydrogenase from Agrobacterium sp

L(-)-Carnitine:NAD+ oxidoreductase, EC 1.1.1.108, from Agrobacterium sp. catalyzes the oxidation of L(-)-carnitine to 3-dehydrocarnitine as initial step of L(-)-carnitine degradation. The enzyme was purified 76-fold by four chromatographic steps. A high substrate specificity for L(-)-carnitine and NAD+ was observed. The molecular mass of the native enzyme is 114 kDa and it consists of two identical subunits as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The isoelectric point was found to be 5.2-5.4. The optimum temperature is 45 degrees C and the optimum pH for the oxidation and the reduction reaction are 9.5 and 5.5-6.5, respectively. Kinetic parameters and amino-terminal sequence were determined. The oxidation reaction is inhibited by D(+)-carnitine, trimethylamine, several metal ions and cetyltrimethylammoniumbromide (CTAB).