Isolation, Purification, and Characterization of a New Enzyme fromPseudomonassp. M-27, Carboxypeptidase G3

In vitro and in silico characterization of a novel glutamate carboxypeptidase from Cohnella sp. A01

Glutamate carboxypeptidase is a bacterial enzyme of metallopeptidase superfamily. This enzyme is an exo-peptidase that catalyzes the hydrolysis of glutamate residues at the C-terminus of folic acid. The rCP302 is a novel zinc ion-dependent recombinant glutamate carboxypeptidase derived from a thermophilic bacterium, Cohnella sp. A01 (PTCC No: 1921). By simulating the structure of rCP302, analyzing its activity in various environmental settings, and contrasting it with that of related enzymes, we wanted to evaluate the heterologous production, purification, and characterization of this enzyme. The bioinformatics study showed that rCP302 had maximum similarity to M20 family of metallopeptidases. The purified rCP302 molecular weight was about 41.6 kDa. The optimum temperature and pH for the catalytic activity of rCP302 were 50 °C and 7.2, respectively. Fluorescence spectroscopy data elucidated the secondary structure of rCP302 and determined conformational changes caused by alterations in ambient conditions. Using folate as a substrate, K_m and specific activity values were calculated as 0.108 μM and 687 μmol/min/mg, respectively. The enzyme activity was strongly inhibited when EDTA sequestered zinc ions. The half-life of this enzyme at 30 °C was 2012 min. Regarding the ability of rCP302 to degrade folic acid, and its long half-life at 37 °C, the normal temperature of many mammals, this enzyme can be introduced for further study for use in the pharmaceutical industry.

The 46 kDa dimeric protein from Variovorax paradoxus shows faster methotrexate degrading activity in its nanoform compare to the native enzyme

Methotrexate degrading enzymes are required to overcome the toxicity of the methotrexate while treating the cancer. The enzyme from Variovorax paradoxus converts the methotrexate in to non toxic products. Methotrexate degrading enzyme from V. paradoxus is a dimeric protein with a molecular mass of 46 kDa and it acts on casein and gelatin. This enzyme is optimally active at pH 7.5 and 40°C and nanoparticles of this enzyme were prepared by desolvation-crosslinking method. Enzyme nanoparticles could degrade methotrexate faster than the native enzyme and they show lower Km compare to the native enzyme. Enzyme nanoparticles show better thermostability and they were stable for much longer time in the serum compare to the native enzyme. Enzyme nanoparticles show better functionality than the native enzyme while clearing the methotrexate added to the serum suggesting their advantage over the native enzyme for the therapeutic and biotechnological applications.

Carboxypeptidase from Streptomyces bikiniensis: primary structure, isolation, and properties

A metallocarboxypeptidase produced by Streptomyces bikiniensis 27 strain (VKPM Ac-1783) (CPSb) was purified and characterized. The enzyme cleaves both basic and hydrophobic C-terminal amino acid residues from synthetic peptides, that is, it possesses specificity of mammalian carboxypeptidases A and B. The enzyme also hydrolyzes peptides bearing glutamic acid at the C-end. CPSb exhibits its maximal activity at pH 7.0-7.6 and 55°C. The nucleotide sequence encoding the mature CPSb in S. bikiniensis 27 (VKPM Ac-1783) genome (Accession No. GU362077) was determined. It is shown that the primary structure of the mature enzyme has a moderate degree of identity with orthologs from Streptomyces griseus (79% identity) and Streptomyces avermitilis (85% identity).

A novel acylase from Streptomyces mobaraensis that efficiently catalyzes hydrolysis/synthesis of capsaicins as well as N-acyl-L-amino acids and N-acyl-peptides

A novel enzyme that catalyzes efficient hydrolysis of capsaicin (8-methyl-N-vanillyl-6-nonenamide) was isolated from the culture broth of Streptomyces mobaraensis. The enzyme consisted of two dissimilar subunits with molecular masses of 61 and 19 kDa. The enzyme was activated and stabilized in the presence of Co2+. It showed a pH optimum of about 8 and was stable at temperatures of up to 55 degrees C for 1 h at pH 7.8. The specific activity of the enzyme for the hydrolysis of capsaicin was 10(2)-10(4) times higher than those for the enzymes reported to date. In an aqueous/n-hexane biphasic system, capsaicin analogues such as octanoyl, decanoyl, and lauroyl vanillylamides were synthesized from the corresponding fatty acids and vanillylamine at yields of 50% or greater. In addition, the enzyme catalyzed the deacylation of N-lauroyl-L-amino acids and N-lauroyl-L-dipeptides and the efficient synthesis of Nalpha-lauroyl-L-lysine, Nepsilon-lauroyl-L-lysine, and various N-lauroyl-peptides in aqueous solution in both the absence and the presence of glycerol.

Crystal structure of carboxypeptidase G2, a bacterial enzyme with applications in cancer therapy

BACKGROUND

Carboxypeptidase G enzymes hydrolyze the C-terminal glutamate moiety from folic acid and its analogues, such as methotrexate. The enzyme studied here, carboxypeptidase G2 (CPG2), is a dimeric zinc-dependent exopeptidase produced by Pseudomonas sp. strain RS-16. CPG2 has applications in cancer therapy: following its administration as an immunoconjugate, in which CPG2 is linked to an antibody to a tumour-specific antigen, it can enzymatically convert subsequently administered inactive prodrugs to cytotoxic drugs selectively at the tumour site. CPG2 has no significant amino acid sequence homology with proteins of known structure. Hence, structure determination of CPG2 was undertaken to identify active-site residues, which may in turn provide ideas for protein and/or substrate modification with a view to improving its therapeutic usefulness.

RESULTS

We have determined the crystal structure of CPG2 at 2.5 A resolution using multiple isomorphous replacement methods and non-crystallographic symmetry averaging. Each subunit of the molecular dimer consists of a larger catalytic domain containing two zinc ions at the active site, and a separate smaller domain that forms the dimer interface. The two active sites in the dimer are more than 60 A apart and are presumed to be independent; each contains a symmetric distribution of carboxylate and histidine ligands around two zinc ions which are 3.3 A apart. This distance is bridged by two shared zinc ligands, an aspartic acid residue and a hydroxyl ion.

CONCLUSIONS

We find that the CPG2 catalytic domain has structural homology with other zinc-dependent exopeptidases, both those with a single zinc ion and those with a pair of zinc ions in the active site. The closest structural homology is with the aminopeptidase from Aeromonas proteolytica, where the similarity includes superposable zinc ligands but does not extend to the rest of the active-site residues, consistent with the different substrate specificities. The mechanism of peptide cleavage is likely to be very similar in these two enzymes and may involve the bridging hydroxyl ion ligand acting as a primary nucleophile.