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

A new type of carboxypeptidase was found in a strain of Pseudomonas sp. M-27 isolated from soil. The cell-free extract, solubilized by colistin sulfate, was purified to homogeneity. This enzyme had a single peak with a molecular weight of 60,000 on a calibrated Superdex column and consisted of four subunits of identical molecular weights (M(r): 15,000). The enzyme hydrolyzed predominantly acidic peptides and N-acyl amino acids with Glu or Asp in the C-termini. This enzyme was not strongly affected by thiol enzyme inhibitors (PCMB, iodoacetic acid) or serine protease inhibitors (DFP, PMSF), but was inhibited by metal chelators. The enzyme resembles carboxypeptidase G1 or G2 in its glutamate-releasing activity. However, it acts not only on the L-form but also on the D-form of acidic amino acids and shows affinity for the long-chain fatty acyl group but not the benzoyl group. Thus, as this enzyme differs from carboxypeptidase G1 or G2, it was named carboxypeptidase G3.

Purification and Characterization of a Thermostable Carboxypeptidase (CarboxypeptidaseTaq)fromThermus aquaticusYT-1

A thermostable carboxypeptidase, which we named carboxypeptidase Taq, was purified from Thermus aquaticus YT-1 and characterized. The molecular weight of the enzyme was estimated to be about 56,000 and 58,000 on SDS-polyacrylamide gel electrophoresis and gel filtration, respectively, indicating that the enzyme has a monomeric structure. The optimum pH of the enzyme was 8.0, and the optimum temperature for the reaction was 80 degrees C. The enzyme activity was dependent on cobalt ion and was inhibited by metal-chelating reagents, indicating that the enzyme is a metalloenzyme. The enzyme had high thermostability independent of cobalt ion; about 90% of its activity remained even after treatment at 80 degrees C for 5 h. The enzyme showed broad substrate specificity, although proline at the C-terminus of peptides was not cleaved. The enzyme released amino acids sequentially from the C-terminus.

Overexpression and Characterization of a Carboxypeptidase from the Hyperthermophilic ArchaeonThermococcussp. NA1

Genomic analysis of a hyperthermophilic archaeon, Thermococcus sp. NA1, revealed the presence of an 1,497 bp open reading frame, encoding a protein of 499 amino acids. The deduced amino acid sequence was similar to thermostable carboxypeptidase 1 from Pyrococcus furiosus, a member of peptidase family M32. Five motifs, including the HEXXH motif with two histidines coordinated with the active site metal, were conserved. The carboxypeptidase gene was cloned and overexpressed in Escherichia coli. Molecular masses assessed by SDS-PAGE and gel filtration were 61 kDa and 125 kDa respectively, which points to a dimeric structure for the recombinant enzyme, designated TNA1_CP. The enzyme showed optimum activity toward Z-Ala-Arg at pH 6.5 and 70-80 degrees C (k(cat)/K(m)=8.3 mM(-1) s(-1)). In comparison with that of P. furiosus CP (k(cat)/K(m)=667 mM(-1) s(-1)), TNA1_CP exhibited 80-fold lower catalytic efficiency. The enzyme showed broad substrate specificity with a preference for basic, aliphatic, and aromatic C-terminal amino acids. This broad specificity was confirmed by C-terminal ladder sequencing of porcine N-acetyl-renin substrate by TNA1_CP.

SUPPRESSOR OF LLP1 1-mediated C-terminal processing is critical for CLE19 peptide activity

Cell-to-cell communication is essential for the coordinated development of multicellular organisms. Members of the CLAVATA3/EMBRYO-SURROUNDING REGION-RELATED (CLE) family, a group of small secretory peptides, are involved in these processes in plants. Although post-translational modifications are considered to be indispensable for their activity, the detailed mechanisms governing these modifications are not well understood. Here, we report that SUPPRESSOR OF LLP1 1 (SOL1), a putative Zn²⁺ carboxypeptidase previously isolated as a suppressor of the CLE19 over-expression phenotype, functions in C-terminal processing of the CLE19 proprotein to produce the functional CLE19 peptide. Newly isolated sol1 mutants are resistant to CLE19 over-expression, consistent with the previous report (Casamitjana-Martinez, E., Hofhuis, H.F., Xu, J., Liu, C.M., Heidstra, R. and Scheres, B. (2003) Curr. Biol. 13, 1435-1441). As expected, our experiment using synthetic CLE19 peptide revealed that the sol1 mutation does not compromise CLE signal transduction pathways per se. SOL1 possesses enzymatic activity to remove the C-terminal arginine residue of CLE19 proprotein in vitro, and SOL1-dependent cleavage of the C-terminal arginine residue is necessary for CLE19 activity in vivo. Additionally, the endosomal localization of SOL1 suggests that this processing occurs in endosomes in the secretory pathway. Thus, our data indicate the importance of C-terminal processing of CLE proproteins to ensure CLE activities.

A digestive prolyl carboxypeptidase in Tenebrio molitor larvae

Prolyl carboxypeptidase (PRCP) is a lysosomal proline specific serine peptidase that also plays a vital role in the regulation of physiological processes in mammals. In this report, we isolate and characterize the first PRCP in an insect. PRCP was purified from the anterior midgut of larvae of a stored product pest, Tenebrio molitor, using a three-step chromatography strategy, and it was determined that the purified enzyme was a dimer. The cDNA of PRCP was cloned and sequenced, and the predicted protein was identical to the proteomic sequences of the purified enzyme. The substrate specificity and kinetic parameters of the enzyme were determined. The T. molitor PRCP participates in the hydrolysis of the insect's major dietary proteins, gliadins, and is the first PRCP to be ascribed a digestive function. Our collective data suggest that the evolutionary enrichment of the digestive peptidase complex in insects with an area of acidic to neutral pH in the midgut is a result of the incorporation of lysosomal peptidases, including PRCP.

Carboxypeptidase I from triticale grains and the hydrolysis of salt-soluble fractions of storage proteins

Carboxypeptidase I was purified from triticale grains (×Triticosecale Wittm.) by a 5-step purification procedure including gel filtration, cation-exchange chromatography and affinity chromatography. The enzyme was purified 595.9 fold with a 1.58% recovery. Triticale carboxypeptidase I is a homodimer with a molecular weight of 124.2 kDa and a subunit weight of 55.2 kDa. Each subunit is composed of two polypeptide chains (33.4 and 21.3 kDa). Serine was found in the active site of triticale carboxypeptidase I; DFP (diisopropylflourophosphate) and other applied inhibitors of serine proteases inhibited the enzyme activity. Triticale carboxypeptidase I hydrolyzes N-CBZ-dipeptide (N-carbobenzoxy-dipeptide) substrates at low pH. N-CBZ-Phe-Ala, N-CBZ-Phe-Leu and N-CBZ-Ala-Met were hydrolyzed with the highest rates. The lowest K(m) value and the highest k(cat)/K(m) ratio were observed for hydrolysis of N-CBZ-Phe-Ala. Studies on the amino acid sequence revealed that the purified enzyme is homologous to carboxypeptidase I from barley. Analyses of conserved regions in the sequence of triticale carboxypeptidase I revealed the presence of Ser, Asp and His that compose the catalytic triad. Intact storage proteins were poor substrates for carboxypeptidases. Carboxypeptidase I together with carboxypeptidase III effectively degraded albumins proteolytically modified by endopeptidase EP8. Modified globulins were degraded at a slower rate, and all three carboxypeptidases were required for a significantly increased activity. Studies of the expression of the carboxypeptidase I gene revealed that the synthesis of the enzyme occurs mainly in the scutellum of the grain. The enzyme is also expressed in the aleurone layer of the grains, although its function in this tissue is unknown.

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).

Isolation and characterization of carboxypeptidase III from germinating triticale grains

Carboxypeptidase III from germinating triticale grains was purified 434.2-fold with a six-step procedure including: homogenization, ammonium sulfate precipitation, cation-exchange chromatography on CM-cellulose, gel filtration chromatography on Sephadex G-150, cation-exchange chromatography on SP8HR column (HPLC), and affinity chromatography on CABSSepharose 4B. Triticale carboxypeptidase III is a monomer with a molecular weight of 45 kDa, which optimally hydrolyzes peptides at temperature 30-50 degrees C and pH 4.6. N-CBZ-Ala-Phe, N-CBZ-Ala-Leu, and N-CBZ-Ala-Met are hydrolyzed at the highest rates. Amino acids with aromatic or large aliphatic side chains are preferred in position P1', whereas the presence of these types of groups in position P1 of the substrate results in a lower rate of hydrolysis. Peptides containing glutamic acid in positions P1 are poor substrates for the enzyme. This phenomenon suggests the hydrophobic substrate- binding sites S1 and S1'. The active site contains serine since diisopropylfluorophosphate and phenylmethanesulfonyl fluoride reduce the activity by 89.9% and 81.5%, respectively. Moreover, the activity of triticale carboxypeptidase III is reduced by mercury ions and organomercurial compounds, which suggests the presence of a sulfhydryl group adjacent to the active site of the enzyme. Identification of purified enzyme by mass spectrometry method demonstrated that the enzyme is a homolog of barley carboxypeptidase III.

A multifunctional human Argonaute2-specific monoclonal antibody

Small regulatory RNAs including small interfering RNAs (siRNAs), microRNAs (miRNAs), or Piwi interacting RNAs (piRNAs) guide regulation of gene expression in many different organisms. The Argonaute (Ago) protein family constitutes the cellular binding partners of such small RNAs and regulates gene expression on the levels of transcription, mRNA stability, or translation. Due to the lack of highly specific and potent monoclonal antibodies directed against the different Ago proteins, biochemical analyses such as Ago complex purification and characterization rely on overexpression of tagged Ago proteins. Here, we report the generation and functional characterization of a highly specific monoclonal anti-Ago2 antibody termed anti-Ago2(11A9). We show that anti-Ago2(11A9) is specific for human Ago2 and detects Ago2 in Western blots as well as in immunoprecipitation experiments. We further demonstrate that Ago2 can be efficiently eluted from our antibody by a competing peptide. Finally, we show that anti-Ago2(11A9) recognizes Ago2 in immunofluorescence experiments, and we find that Ago2 not only localizes to cytoplasmic processing bodies (P-bodies) and the diffuse cytoplasm but also to the nucleus. With the anti-Ago2(11A9) antibody we have generated a potent tool that is useful for many biochemical or cell biological applications.

[Preparation and characterization of rabbit antibody against human mast cell carboxypeptidase]

AIM

To prepare antibody against human mast cell carboxypeptidase (hMC-CP) by using recombinant hMC-CP expressed in E.coli, and to characterize the antibody.

METHODS

hMC-CP was expressed in E.coli with L-Arabinose induction and purified through Ni-NTA column. The purified hMC-CP as immunogen was used to immunize rabbit. The titer and the specificity of the rabbit anti-hMC-CP antibody was analyzed by indirect ELISA and Western blot respectively.

RESULTS

The hMC-CP was successfully expressed and purified. The polyconal anit-hMC-CP antibody was prepared by immunizing rabbit using the purified recombinant protein, The titer of the generated antiserum was 1:6 400 by ELISA. Western blot analysis showed that this antibody could bind with hMC-CP specifically.

CONCLUSION

The rabbit anti-hMC-CP antibody with high titer and high specificity has been prepared by using purified recombinant hMC-CP as immunogen, which lays the foundation for further research on detection and function of hMC-CP.

Cloning and sequencing of cDNA and genomic DNA encoding serine carboxypeptidase of Fusarium moniliforme that was copurified with phosphatase

A previous study [Yoshida, H. et al., J. Biochem., 140, 813-823 (2006)] revealed that a protein of unknown nature was copurified with PDM phosphatase of Fusarium moniliforme. In this study, the identity of this protein was investigated. The results of homology search for the tryptic peptides derived from the purified preparation of PDM phosphatase strongly suggested that it might be serine carboxypeptidase. In fact, carboxypeptidase activity was demonstrated in the preparation and partial separation of carboxypeptidase from PDM phosphatase was achieved by gel filtration high-performance liquid chromatography. Cloning and sequencing of the full-length cDNA encoding the carboxypeptidase was successfully conducted. The cDNA possessed an open reading frame for a protein of 575 amino acid residues with a molecular mass of 64,650 Da, which was highly homologous to certain fungal serine carboxypeptidases. Comparison of the deduced amino acid sequence with the N-terminal sequence of the separated carboxypeptidase revealed that the mature enzyme starts at serine 56 of the precursor and has a molecular mass of 58,487 Da. Cloning and sequencing of the genomic DNA corresponding to the cDNA demonstrated that the gene of carboxypeptidase consists of four exons. A limited number of close homologs of F. moniliforme carboxypeptidase were detected among fungi by homology search and their evolutionary relationship was discussed.

Characterization of a bifunctional aminoacylase/carboxypeptidase from radioresistant bacterium Deinococcus radiodurans R1

The gene encoding a Deinococcus radiodurans R1 bifunctional aminoacylase/carboxypeptidase (DR_ACY/CP) was amplified by polymerase chain reaction and cloned into pQE-30 to generate pQE-DRAC. The cloned gene consists of an open reading frame of 1197 bp encoding a protein with a molecular mass of 42,729 Da. The predicted amino acid sequence shows high homology with those of Geobacillus kaustophilus aminoacylase, Geobacillus stearothermophilus aminoacylase, Pyrococcus horikoshii carboxypeptidase/aminoacylase and Thermoanaerobacter tengcongensis aminoacylase/carboxypeptidase. The expressed enzyme was purified from the crude extract of IPTG-induced Escherichia coli M15 (pQE-DRAC) to homogeneity by nickel-chelate chromatography. The molecular mass of the purified enzyme was determined to be 43kDa by SDS-PAGE. Maximal aminoacylase activity with N-acetyl-methionine as the substrate occurred at pH 8.0 and 40 degrees C in the sodium phosphate buffer. The aminoacylase activity was strongly inhibited by metal-chelating agents, and was largely restored by divalent cations, such as Co(2+), Mn(2+) and Ni(2+). The purified enzyme had broad specificity toward N-acetylated L-amino acids as well as N-CBZ-peptides. Carboxypeptidase activity of DR_ACY/CP to N-CBZ-Gly-Ala exhibited K(m) and k(cat) values of 4.3mM and 28s(-1), respectively. The enzyme also had activity toward the cell wall-related substrates, D-Ala-Gly, D-Ala-Gly-Gly and L-Orn-L-Ala.

A novel subfamily of mouse cytosolic carboxypeptidases

Nna1 is a recently described gene product that has sequence similarity with metallocarboxypeptidases. In the present study, five additional Nna1-like genes were identified in the mouse genome and named cytosolic carboxypeptidase (CCP) 2 through 6. Modeling suggests that the carboxypeptidase domain folds into a structure that resembles metallocarboxypeptidases of the M14 family, with all necessary residues for catalytic activity and broad substrate specificity. All CCPs are abundant in testis and also expressed in brain, pituitary, eye, and other mouse tissues. In brain, Nna1/CCP1, CCP5, and CCP6 are broadly distributed, whereas CCP2 and 3 exhibit restricted patterns of expression. Nna1/CCP1, CCP2, CCP5, and CCP6 were found to exhibit a cytosolic distribution, with a slight accumulation of CCP5 in the nucleus. Based on the above results, we hypothesized that Nna1/CCP1 and CCP2-6 function in the processing of cytosolic proteins such as alpha-tubulin, which is known to be modified by the removal of a C-terminal tyrosine. Analysis of the forms of alpha tubulin in the olfactory bulb of mice lacking Nna1/CCP1 showed the absence of the detyrosinylated form in the mitral cells. Taken together, these results are consistent with a role for Nna1/CCP1 and the related CCPs in the processing of tubulin.

Two metallocarboxypeptidases from the protozoan Trypanosoma cruzi belong to the M32 family, found so far only in prokaryotes

MCPs (metallocarboxypeptidases) of the M32 family of peptidases have been identified in a number of prokaryotic organisms, and only a few of them have been characterized biochemically. Members of this family are absent from eukaryotic genomes, with the remarkable exception of those of trypanosomatids. The genome of the CL Brener clone of Trypanosoma cruzi, the causative agent of Chagas' disease, encodes two such MCPs, with 64% identity between them: TcMCP-1 and TcMCP-2. Both genes, which are present in a single copy per haploid genome, were expressed in Escherichia coli as catalytically active polyHis-tagged recombinant enzymes. Despite their identity, the purified TcMCPs displayed marked biochemical differences. TcMCP-1 acted optimally at pH 6.2 on FA {N-(3-[2-furyl]acryloyl)}-Ala-Lys with a K(m) of 166 muM. Activity against benzyloxycarbonyl-Ala-Xaa substrates revealed a P1' preference for basic C-terminal residues. In contrast, TcMCP-2 preferred aromatic and aliphatic residues at this position. The K(m) value for FA-Phe-Phe at pH 7.6 was 24 muM. Therefore the specificities of both MCPs are complementary. Western blot analysis revealed a different pattern of expression for both enzymes: whereas TcMCP-1 is present in all life cycle stages of T. cruzi, TcMCP-2 is mainly expressed in the stages that occur in the invertebrate host. Indirect immunofluorescence experiments suggest that both proteins are localized in the parasite cytosol. Members of this family have been identified in other trypanosomatids, which so far are the only group of eukaryotes encoding M32 MCPs. This fact makes these enzymes an attractive potential target for drug development against these organisms.

A vitellogenic-like carboxypeptidase expressed by human macrophages is localized in endoplasmic reticulum and membrane ruffles

Carboxypeptidase, vitellogenic-like (CPVL) is a serine carboxypeptidase of unknown function that was first characterized in human macrophages. Initial studies suggested that CPVL is largely restricted to the monocytic lineage, although it may also be expressed by cells outside the immune system. Here, we use a new monoclonal antibody to characterize the properties and localization of CPVL in human macrophages to elucidate a possible function for the protease. CPVL is up-regulated during the maturation of monocytes (MO) to macrophages, although the protein can be seen in both. In primary macrophages, CPVL is glycosylated with high mannose residues and colocalizes with markers for endoplasmic reticulum, while in MO it is more disperse and less clearly associated with endoplasmic reticulum. CPVL is highly expressed in lamellipodia and membrane ruffles, which also concentrate markers of the secretory pathway (MIP-1alpha and tumour necrosis factor-alpha) and major histocompatibility complex (MHC) class I and II molecules. CPVL can be seen on early latex bead and Candida albicans phagosomes, but it is not retained in the maturing phagosome, unlike MHC class I/II. CPVL has a mixed cytosolic and membrane-associated localization but is not detectable on the outer plasma membrane. We propose that CPVL may be involved in antigen processing, the secretory pathway and/or in actin remodelling and lamellipodium formation.

Structural basis of the resistance of an insect carboxypeptidase to plant protease inhibitors

Corn earworm (Helicoverpa zea), also called tomato fruitworm, is a common pest of many Solanaceous plants. This insect is known to adapt to the ingestion of plant serine protease inhibitors by using digestive proteases that are insensitive to inhibition. We have now identified a B-type carboxypeptidase of H. zea (CPBHz) insensitive to potato carboxypeptidase inhibitor (PCI) in corn earworm. To elucidate the structural features leading to the adaptation of the insect enzyme, the crystal structure of the recombinant CPBHz protein was determined by x-ray diffraction. CPBHz is a member of the A/B subfamily of metallocarboxypeptidases, which displays the characteristic metallocarboxypeptidase alpha/beta-hydrolase fold, and does not differ essentially from the previously described Helicoverpa armigera CPA, which is very sensitive to PCI. The data provide structural insight into several functional properties of CPBHz. The high selectivity shown by CPBHz for C-terminal lysine residues is due to residue changes in the S1' substrate specificity pocket that render it unable to accommodate the side chain of an arginine. The insensitivity of CPBHz to plant inhibitors is explained by the exceptional positioning of two of the main regions that stabilize other carboxypeptidase-PCI complexes, the beta8-alpha9 loop, and alpha7 together with the alpha7-alpha8 loop. The rearrangement of these two regions leads to a displacement of the active-site entrance that impairs the proper interaction with PCI. This report explains a crystal structure of an insect protease and its adaptation to defensive plant protease inhibitors.

The carboxyterminal processing protease of D1 protein: expression, purification and enzymology of the recombinant and native spinach proteins

The carboxyterminal processing protease of D1 protein (CtpA) is predicted to be an excellent target for a general broad-spectrum herbicide. The gene for spinach CtpA has been expressed in Escherichia coli. The expressed protein that was found mainly in inclusion bodies has been purified and refolded on a nickel-chelate column. Active recombinant CtpA was recovered. Two assays for CtpA activity were developed, a medium-throughput HPLC assay using a fluorescent substrate and a high-throughput assay based on fluorescence polarization capable of application in a high-throughput 96-well plate format. This high-throughput assay was developed to screen chemistry for CtpA inhibitors. Native spinach CtpA was partially purified and the native and recombinant enzymes were compared kinetically for their K(m) and V(max) values using different peptide substrates. Native CtpA partially purified from spinach was shown to have similar kinetic properties to recombinant CtpA. Antibodies developed against the recombinant protein were used to estimate the in planta abundance of the native enzyme in spinach. Since only a small proportion of the recombinant protein is refolded during isolation and it appears that only a small proportion of this enzyme is active, size-exclusion chromatography and light scattering experiments were performed on rCtpA in order to gain insight into its structure and the reasons why most of the protein is not active. The use of rCtpA to screen for herbicidal compounds and the more general question of how good a herbicide target the enzyme is are discussed.

Purification and characterization of a high molecular mass serine carboxypeptidase from Monascus pilosus

Two serine carboxypeptidases, MpiCP-1 and MpiCP-2, were purified to homogeneity from Monascus pilosus IFO 4480. MpiCP-1 is a homodimer with a native molecular mass of 125 kDa composed of two identical subunits of 61 kDa, while MpiCP-2 is a high mass homooligomer with a native molecular mass of 2,263 kDa composed of about 38 identical subunits of 59 kDa. This is unique among carboxypeptidases and distinguishes MpiCP-2 as the largest known carboxypeptidase. The two purified enzymes were both acidic glycoproteins. MpiCP-1 has an isoelectric point of 3.7 and a carbohydrate content of 11%, while for MpiCP-2 these values were 4.0 and 33%, respectively. The optimum pH and temperature were around 4.0 and 50 degrees C for MpiCP-1, and 3.5 and 50 degrees C for MpiCP-2. MpiCP-1 was stable over a broad range of pH between 2.0 and 8.0 at 37 degrees C for 1 h, and up to 55 degrees C for 15 min at pH 6.0, but MpiCP-2 was stable in a narrow range of pH between 5.5 and 6.5, and up to 50 degrees C for 15 min at pH 6.0. Phenylmethylsulfonylfluoride strongly inhibited MpiCP-1 and completely inhibited MpiCP-2, suggesting that they are both serine carboxypeptidases. Of the substrates tested, benzyloxycarbonyl-L: -tyrosyl-L: -glutamic acid (Z-Tyr-Glu) was the best for both enzymes. The Km, Vmax, Kcat and Kcat/Km values of MpiCP-1 for Z-Tyr-Glu at pH 4.0 and 37 degrees C were 1.33 mM, 1.49 mM min(-1), 723 s(-1) and 545 mM(-1) s(-1), and those of MpiCP-2 at pH 3.5 and 37 degrees C were 1.55 mM, 1.54 mM min(-1), 2,039 s(-1) and 1,318 mM(-1) s(-1), respectively.

Purification and characterization of a serine carboxypeptidase from Kluyveromyces marxianus

We purified a carboxypeptidase (CPY) from the yeast of Kluyveromyces marxianus. This enzyme was purified 170 times from a soluble extract of 100000 x g. Purification consisted in a fractionated precipitation with ammonium sulfate and two chromatographic steps consisting of anion exchange chromatography and hydrophobic interactions chromatography. The native enzyme depicted a molecular mass of 67 kDa by gel filtration. This serine carboxypeptidase depicted an optimal pH of 8.5 and was stable at a pH ranging from 6.0 to 9.0, its optimal temperature was of 45 degrees C and was unstable at temperatures above 55 degrees C; Michaelis constant and Vmax for N-benzoyl-l-tyrosine-p-nitroanilide were of 29 microM and 612 microM/min mg of protein, respectively. The enzyme was strongly inhibited by phenylmethylsufonyl fluoride (PMSF) and, to a lesser degree, by trans-epoxysuccinyl-l-leucylamido-(4-guanidine)-butane. This study indicated that K. marxianus carboxypeptidase could be an alternative to other animal-source carboxypeptidases in the industry.

Purification and characterization of a new type of serine carboxypeptidase from Monascus purpureus

Carboxypeptidase produced by Monascus purpureus IFO 4478 was purified to homogeneity. The purified enzyme is a heterodimer with a molecular mass of 132 kDa and consists of two subunits of 64 and 67 kDa. It is an acidic glycoprotein with an isoelectric point of 3.67 and 17.0% carbohydrate content. The optimum pH and temperature were 4.0 and 40 degrees C, respectively. The enzyme was stable between pH 2.0 and 8.0 at 37 degrees C for 1 h, and up to 50 degrees C at pH 5.0 for 15 min. The enzyme was strongly inhibited by piperastatin A, diisopropylfluoride phosphate (DFP), phenylmethylsulfonylfluoride (PMSF), and chymostatin, suggesting that it is a chymotrypsin-like serine carboxypeptidase. Monascus purpureus carboxypeptidase was also strongly inhibited by p-chloromercuribenzoic acid (PCMB) but not by ethylenediaminetetraacetic acid (EDTA) and 1,10-phenanthroline, indicating that it requires cysteine residue but not metal ions for activity. Benzyloxycarbonyl- l-tyrosyl- l-glutamic acid (Z-Tyr-Glu), among the substrates tested, was the best substrate of the enzyme. The K(m), V(max), K(cat), and K(cat) /K(m) values of the enzyme for Z-Tyr-Glu at pH 4.0 and 37 degrees C were 0.86 mM, 0.917 mM min(-1), 291 s(-1), and 339 mM(-1 )s(-1), respectively.

New serine carboxypeptidase in mung bean seedling cotyledons

Two serine carboxypeptidases (EC 3.4.16.5) were purified from mung bean seedling cotyledons. Sequences of tryptic peptides derived from the 42.5 kD enzyme corresponded to the derived amino acid sequence of a sequenced cDNA (GenBank U49382 and U49741). This enzyme exhibited the substrate specificity pattern previously published for mung bean carboxypeptidase I. In comparison, the sequence and substrate specificity data obtained for the 43 kD enzyme were similar but not identical. Both enzymes showed preference for peptide substrates with a large hydrophobic residue at the C-terminus. With regard to the penultimate residue of peptide substrates, the mung bean carboxypeptidase I preferred small aliphatic amino acid residues, while the 43 kD enzyme preferred large hydrophobic ones.

Characterization of a lysosomal serine carboxypeptidase from Trypanosoma cruzi

Trypanosoma cruzi, the flagellate protozoan which is the causative agent of the American trypanosomiasis, Chagas disease has carboxypeptidase activity. The enzyme has been purified to protein homogeneity, and shown to be a lysosomal monomeric glycoprotein with a molecular mass of about 54kDa. The enzyme has an optimum acidic pH (4.5 with furyl acryloyl-Phe-Phe as substrate), is highly specific for hydrophobic C-terminal amino acid residues, and is strongly inhibited by 3,4-dichloroisocoumarin (IC(50) value 0.3 microM). The enzyme is encoded by a number of genes arrayed in head-to-tail tandems; one of these genes has been cloned and sequenced. Sequence comparisons indicate that the enzyme belongs to the C group of serine carboxypeptidases, within the S10 serine peptidase family, and shows the higher similarity to plant and yeast enzymes. The residues involved in catalysis and most of those involved in substrate binding are conserved in the T. cruzi enzyme as well as 8 out of 10 Cys residues known to be involved in disulfide bridges in the yeast enzyme. This is the first report of an S10 family enzyme in trypanosomatids. The presence of serine carboxypeptidases is not restricted to T. cruzi, being possibly a general character of trypanosomatids.

Isolation, partial purification, characterization, and tissue distribution of phenylmethylsulfonyl fluoride-inhibited feline carboxypeptidase

Phenylmethylsulfonyl fluoride (PMSF)-inhibited carboxypeptidase from cat liver was purified 148-fold by chromatography on CM- and DEAE-cellulose with 27.3% yield. Molecular weight of the enzyme is 100-110 kD as determined by gel filtration on Sephadex G-150. The enzyme has maximum activity at pH 5.50-5.75; its activity is completely inhibited by PMSF or p-chloromercuribenzoate and partially inhibited by iodoacetamide. EDTA, 2-mercaptoethanol, N-ethylmaleimide, Co(2+) and Ca2+, basic carboxypeptidase inhibitor guanidinoethylmercaptosuccinic acid, and angiotensin-converting enzyme inhibitor captopril do not influence its activity. The enzyme cleaves arginine from enkephalin-Leu5-Arg6 and dansyl-Phe-Leu-Arg to form enkephalin-Leu5 and dansyl-Phe-Leu, respectively, and very slowly cleaves leucine from carbobenzoxy-Gly-Leu. Further cleavage of either enkephalin-Leu5 or dansyl-Phe-Leu was not detected. The highest activity of this enzyme was found in adrenal glands and testicles; this activity was 30% lower in hypophysis, and still lower in liver and kidney. The PMSF-inhibited carboxypeptidase activity in brain was about 6-16 times lower than that in adrenal gland. In brain regions, the highest activity was detected in gray matter of cerebral hemispheres and cerebellum, and slightly lower activity was found in thalamus/hypothalamus, striatum, and hippocampus. The lowest activity was found in quadrigeminal bodies, medulla oblongata, and white matter of cerebral hemispheres. The enzyme exists mainly in soluble form; the activity of membrane-associated enzyme is 7-25% of soluble enzyme activity depending on tissue type. We consider here a possible involvement of PMSF-inhibited carboxypeptidase in the metabolism of biologically active peptides.

Isolation and characteristics of carboxypeptidase B from the pyloric ceca of the starfish Asterias amurensis

Carboxypeptidase B was purified from the pyloric ceca of the starfish Asterias amurensis. The final enzyme preparation was nearly homogeneous in polyacrylamide gel electrophoresis and its molecular weight was estimated as approximately 34,000. The optimum pH and temperature of the enzyme for hydrolysis of benzoyl-glycyl-L-arginine were at approximately pH 7.5 and 55 degrees C, respectively. The enzyme was unstable at above 50 degrees C and at below pH 5.0. The enzyme was activated by Co(2+), but was inhibited by EDTA and Hg(2+). The N-terminal amino acid sequence of A. amurensis carboxypeptidase B was ASFDYNVYHSYQEIMNWITN.

CPG70 is a novel basic metallocarboxypeptidase with C-terminal polycystic kidney disease domains from Porphyromonas gingivalis

In a search for a basic carboxypeptidase that might work in concert with the major virulence factors, the Arg- and Lys-specific cysteine endoproteinases of Porphyromonas gingivalis, a novel 69.8-kDa metallocarboxypeptidase CPG70 was purified to apparent homogeneity from the culture fluid of P. gingivalis HG66. Carboxypeptidase activity was measured by matrix-assisted laser desorption ionization-mass spectrometry using peptide substrates derived from a tryptic digest of hemoglobin. CPG70 exhibited activity with peptides containing C-terminal Lys and Arg residues. The k(cat)/K(m) values for the hydrolysis of the synthetic dipeptides FA-Ala-Lys and FA-Ala-Arg by CPG70 were 99 and 56 mm(-1)s(-1), respectively. The enzyme activity was strongly inhibited by the Arg analog (2-guanidinoethylmercapto)succinic acid and 1,10-phenanthroline. High resolution inductively coupled plasma-mass spectrometry demonstrated that 1 mol of CPG70 was associated with 0.6 mol of zinc, 0.2 mol of nickel, and 0.2 mol of copper. A search of the P. gingivalis W83 genomic data base (TIGR) with the N-terminal amino acid sequence determined for CPG70 revealed that the enzyme is an N- and C-terminally truncated form of a predicted 91.5-kDa protein (PG0232). Analysis of the deduced amino acid sequence of the full-length protein revealed an N-terminal signal sequence followed by a pro-segment, a metallocarboxypeptidase catalytic domain, three tandem polycystic kidney disease domains, and an 88-residue C-terminal segment. The catalytic domain exhibited the highest sequence identity with the duck metallocarboxypeptidase D domain II. Insertional inactivation of the gene encoding CPG70 resulted in a P. gingivalis isogenic mutant that was avirulent in the murine lesion model under the conditions tested.

ACEH/ACE2 is a novel mammalian metallocarboxypeptidase and a homologue of angiotensin-converting enzyme insensitive to ACE inhibitors

A human zinc metalloprotease (termed ACEH or ACE2) with considerable homology to angiotensin-converting enzyme (ACE) (EC 3.4.15.1) has been identified and subsequently cloned and functionally expressed. The translated protein contains an N-terminal signal sequence, a single catalytic domain with zinc-binding motif (HEMGH), a transmembrane region, and a small C-terminal cytosolic domain. Unlike somatic ACE, ACEH functions as a carboxypeptidase when acting on angiotensin I and angiotensin II or other peptide substrates. ACEH may function in conjunction with ACE and neprilysin in novel pathways of angiotensin metabolism of physiological significance. In contrast with ACE, ACEH does not hydrolyse bradykinin and is not inhibited by typical ACE inhibitors. ACEH is unique among mammalian carboxypeptidases in containing an HEXXH zinc motif but, in this respect, resembles a bacterial enzyme, Thermus aquaticus (Taq) carboxypeptidase (EC 3.4.17.19). Collectrin, a developmentally regulated renal protein, is homologous with the C-terminal region of ACEH but has no similarity with ACE and no catalytic domain. Thus, the ACEH protein may have evolved as a chimera of a single ACE-like domain and a collectrin domain. The collectrin domain may regulate tissue response to injury whereas the catalytic domain is involved in peptide processing events.

Substrate specificity, inhibition and enzymological analysis of recombinant human glutamate carboxypeptidase II

Glutamate carboxypeptidase II (GCPII, EC 3.4.17.21) is a membrane peptidase expressed in a number of tissues such as kidney, prostate and brain. The brain form of GCPII (also known as NAALADase) cleaves N-acetyl-aspartyl glutamate to yield free glutamate. Animal model experiments show that inhibition of GCPII prevents neuronal cell death during experimental ischaemia. GCPII thus represents an important target for the treatment of neuronal damage caused by excess glutamate. In this paper we report expression of an extracellular portion of human glutamate carboxypeptidase II (amino acids 44-750) in Drosophila Schneider's cells and its purification to homogeneity. A novel assay for hydrolytic activity of recombinant human GCPII (rhGCPII), based on fluorimetric detection of released alpha-amino groups was established, and used for its enzymological characterization. rhGCPII does not show dipeptidylpeptidase IV-like activity assigned to the native form of the enzyme previously. Using a complete set of protected dipeptides, substrate specificity of rhGCPII was elucidated. In addition to the previously described substrates, four novel compounds, Ac-Glu-Met, Ac-Asp-Met and, surprisingly, Ac-Ala-Glu and Ac-Ala-Met were identified as substrates for GCPII, and their respective kinetic constants determined. The glycosylation of rhGCPII was found indispensable for the enzymatic activity.

[Cloning and expression of extracellular domain of prostate specific membrane antigen in Escherichia coli and preparation of polyclonal antibody]

Human Prostate Specific Membrane Antigen(PSMA) cDNA was amplified using total RNA extracted from prostate carcinoma tissue by RT-PCR. The cDNA fragment of extracellular domain of PSMA(edPSMA) gene was amplified by PCR and cloned into expression vector pMAL-c2x. Sequence analysis of both PSMA and edPSMA revealed identity to the GenBank reported. The edPSMA was expressed in E. coli as part of a fusion protein with MBP as the induction of IPTG. Western blot analysis showed the recombinant protein could react with PSMA monocloned antibodies 4G5. MBP-edPSMA fusion protein were purified by amylose resin affinity chromatography and showed to be homogeneity in SDS-PAGE(120 kD). BALB/C mice were immunized with the purified protein for the preparation of polyclonal antibody. The polyclonal antibody, which had a title of 1:12,800, were indicated the specificity to prostate tissue.

Purification and characterization of a carboxypeptidase from squid hepatopancreas (Illex illecebrosus)

The hepatopancreas of squid (Illex illecebrosus) extract contains a wide range of carboxypeptidase (CP) activities based on hydrolysis of N-CBZ-dipeptide substrates. SDS-PAGE zymograms with N-CBZ-Phe-Leu substrate revealed three activity zones (CP-I, 23 kDa; CP-II, 29 kDa; CP-III, 42 kDa). CP-I was purified 225-fold with 86.20% recovery based on N-CBZ-Ala-Phe activity by chromatography on DEAE-cellulose, gel filtration, and chromatofocusing. The purified enzyme had broad specificity toward N-CBZ-dipeptides; however, it preferred substrates with a hydrophobic amino acid at the C terminus. CP-I had greatest activity with N-CBZ-Ala-Phe (specific activity = 7104 units/mg of protein, K(m) = 0.40 mM, and physiological efficiency = 22863). CP-I had a pI of 3.4 and is a metalloprotease that is activated by Co(2+) and partially inhibited by Pefabloc, a serine protease inhibitor. With N-CBZ-Ala-Phe and Gly-Phe, it had optimum activity at pH 8 and 70 degrees C. The amino acid composition of squid CP-I is similar to that of CP A from other species.

Immunohistochemical localization and comparison of carboxypeptidases D, E, and Z, alpha-MSH, ACTH, and MIB-1 between human anterior and corticotroph cell "basophil invasion" of the posterior pituitary

Basophil invasion, i.e., invasion of basophilic corticotrophs from the residual intermediate lobe into the posterior lobe of the human pituitary gland, is believed to be a physiological phenomenon. This study evaluated the distribution of CPE, CPD, CPZ, alpha-MSH, ACTH, and Ki-67 immunoreactivity between human anterior pituitary and basophil invasion of the neurohypophysis. Mild to moderate immunoreactivities for CPE and CPZ were distributed relatively uniformly in the majority of the anterior pituitary cells and basophil invasion. In contrast, only corticotrophs exhibited intense CPD immunoreactivity. Basophil invasion showed similar immunoreactivities for alpha-MSH, ACTH, CPE, and CPZ as corticotrophs in the anterior pituitary, except for CPD, which was detected much less frequently. In the posterior lobe, CPE, CPD, and CPZ were present within the Herring bodies. Although no MIB-1 immunoreactivity was identified in anterior pituitary cells, limited MIB-1 labeling was detected in basophil invasion in five of ten cases. Highly selective expression of CPD in corticotrophs suggests that CPD plays a particularly important role in prohormone (POMC) processing in corticotrophs, with minimal or no significant roles in non-corticotrophs. Evidence that corticotrophs in basophil invasion are undergoing proliferation and are also phenotypically different from their counterpart in the anterior pituitary has further raised the possibility of some neoplastic potential.

Refolding and purification of yeast carboxypeptidase Y expressed as inclusion bodies in Escherichia coli

The genes encoding carboxypeptidase Y (CPY) and CPY propeptide (CPYPR) from Saccharomyces cerevisiae were cloned and expressed in Escherichia coli. Six consecutive histidine residues were fused to the C-terminus of the CPYPR for facilitated purification. High-level expression of CPY and CPYPR-His(6) was achieved but most of the expressed proteins were present in the form of inclusion bodies in the bacterial cytoplasm. The CPY and CPYPR-His(6) produced as inclusion bodies were separated from the cells and solubilized in 6 and 3 M guanidinium chloride, respectively. The denatured CPYPR-His(6) was refolded by dilution 1:30 into the renaturation buffer (50 mM Tris-HCl containing 0.5 M NaCl and 3 mM EDTA, pH 8.0), and the refolded CPYPR-His(6) was further purified to 90% purity by single-step immobilized metal ion affinity chromatography. The denatured CPY was refolded by dilution 1:60 into the renaturation buffer containing CPYPR-His(6) at various concentrations. Increasing the molar ratio of CPYPR-His(6) to CPY resulted in an increase in the CPY refolding yield, indicating that the CPYPR-His(6) plays a chaperone-like role in in vitro folding of CPY. The refolded CPY was purified to 92% purity by single-step p-aminobenzylsuccinic acid affinity chromatography. When refolding was carried out in the presence of 10 molar eq CPYPR-His(6), the specific activity, N-(2-furanacryloyl)-l-phenylalanyl-l-phenylalanine hydrolysis activity per milligram of protein, of purified recombinant CPY was found to be about 63% of that of native S. cerevisiae CPY.

Thrombin activatable fibrinolysis inhibitor and an antifibrinolytic pathway

Coagulation and fibrinolysis are processes that form and dissolve fibrin, respectively. These processes are exquisitely regulated and protect the organism from excessive blood loss or excessive fibrin deposition. Regulation of these cascades is accomplished by a variety of mechanisms involving cellular responses, flow, and protein-protein interactions. With respect to regulation mediated by protein-protein interaction, the coagulation cascade appears to be more complex than the fibrinolytic cascade because it has more components. Yet each cascade is regulated by initiators, cofactors, feedback reactions, and inhibitors. Coagulation is also controlled by an anticoagulant pathway composed of (minimally) thrombin, thrombomodulin, and protein C.(1) Protein C is converted by the thrombin/thrombomodulin complex to activated protein C (APC), which catalyzes the proteolytic inactivation of the essential cofactors required for thrombin formation, factors Va and VIIIa. An analogous antifibrinolytic pathway has been identified recently. This pathway provides an apparent symmetry between coagulation and fibrinolysis and is also composed of thrombin, thrombomodulin, and a zymogen that is activated to an enzyme. The enzyme proteolytically inactivates a cofactor to attenuate fibrinolysis. However, unlike APC, which is a serine protease, the antifibrinolytic enzyme is a metalloprotease that exhibits carboxypeptidase B-like activity. Within a few years of each other, 5 groups independently described a molecule that accounts for this antifibrinolytic activity. We refer to this molecule as thrombin activatable fibrinolysis inhibitor (TAFI), a name that is based on functional properties by which it was identified, assayed, and purified. (Because of the preferences of some journals "activatable" is occasionally referred to as "activable.") This review will encompass a historical account of efforts to isolate TAFI and characterize it with respect to its activation, activity, regulation, and potential function in vivo.

Biochemical characterization of human cathepsin X revealed that the enzyme is an exopeptidase, acting as carboxymonopeptidase or carboxydipeptidase

Cathepsin X, purified to homogeneity from human liver, is a single chain glycoprotein with a molecular mass of approximately 33 kDa and pI 5.1-5.3. Cathepsin X was inhibited by stefin A, cystatin C and chicken cystatin (Ki = 1.7-15.0 nM), but poorly or not at all by stefin B (Ki > 250 nM) and L-kininogen, respectively. The enzyme was also inhibited by two specific synthetic cathepsin B inhibitors, CA-074 and GFG-semicarbazone. Cathepsin X was similar to cathepsin B and found to be a carboxypeptidase with preference for a positively charged Arg in P1 position. Contrary to the preference of cathepsin B, cathepsin X normally acts as a carboxymonopeptidase. However, the preference for Arg in the P1 position is so strong that cathepsin X cleaves substrates with Arg in antepenultimate position, acting also as a carboxydipeptidase. A large hydrophobic residue such as Trp is preferred in the P1' position, although the enzyme cleaved all P1' residues investigated (Trp, Phe, Ala, Arg, Pro). Cathepsin X also cleaved substrates with amide-blocked C-terminal carboxyl group with rates similar to those of the unblocked substrates. In contrast, no endopeptidase activity of cathepsin X could be detected on a series of o-aminobenzoic acid-peptidyl-N-[2,-dinitrophenyl]ethylenediamine substrates. Furthermore, the standard cysteine protease methylcoumarine amide substrates (kcat/Km approximately 5.0 x 103 M-1.s-1) were degraded approximately 25-fold less efficiently than the carboxypeptidase substrates (kcat/Km approximately 120.0 x 103 M-1.s-1).

Generation of a baculovirus recombinant prostate-specific membrane antigen and its use in the development of a novel protein biochip quantitative immunoassay

Prostate-specific membrane antigen (PSMA) is a 100-kDa transmembrane glycoprotein identified by the monoclonal antibody 7E11-C5.3 from the human prostate tumor cell line LNCaP. Because of its significant upregulation in androgen refractory and metastatic prostate cancers, PSMA may be a useful prognostic biomarker and a target for developing novel therapeutic strategies. However, the lack of abundant pure PSMA protein and the low efficacy in immunoaffinity isolation from LNCaP cells have hampered the development of clinical assays. In order to obtain a renewable and reliable source of pure antigen, we used the baculovirus/insect cell system to express and purify a recombinant PSMA. A recombinant baculovirus containing a 6x histidine-tagged PSMA gene was generated, from which rPSMA was expressed and purified using cobalt-chelating affinity chromatography. The purity and correct molecular size of rPSMA were demonstrated by gel electrophoresis and mass spectrometry. Glycosidase digestions showed that the oligosaccharides on rPSMA are primarily N-linked high-mannose type. Although the glycosylation is different from the native PSMA, it did not affect the immunoreactivity of rPSMA to antibodies specific for either the intra- or the extracellular domains of PSMA. Finally, the purified rPSMA was successfully used to develop a quantitative PSMA immunoassay using the novel ProteinChip surface-enhanced laser desorption/ionization mass spectrometry technology.

Receptor recognition by a hepatitis B virus reveals a novel mode of high affinity virus-receptor interaction

The duck hepatitis B virus model system was used to elucidate the characteristics of receptor (carboxypeptidase D, gp180) interaction with polypeptides representing the receptor binding site in the preS part of the large viral surface protein. We demonstrate the pivotal role of carboxypeptidase D for virus entry and show its C-domain represents the virus attachment site, which binds preS with extraordinary affinity. Combining results from surface plasmon resonance spectroscopy and two-dimensional NMR analysis we resolved the contribution of preS sequence elements to complex stability and show that receptor binding potentially occurs in two steps. Initially, a short alpha-helix in the C-terminus of the receptor binding domain facilitates formation of a primary complex. This complex is stabilized sequentially, involving approximately 60 most randomly structured amino acids preceding the helix. Thus, hepadnaviruses exhibit a novel mechanism of high affinity receptor interaction by conserving the potential to adapt structure during binding rather than to preserve it per se. We propose that this process represents an alternative strategy to escape immune surveillance and the evolutionary pressure inherent in the compact hepadnaviral genome organization.

Proteolytic activation of purified human procarboxypeptidase U

Carboxypeptidase U (CPU, EC 3.4.17.20) is a recently described basic carboxypeptidase which circulates in plasma as an enzymatically inactive precursor procarboxypeptidase U (proCPU), also known as plasma carboxypeptidase B precursor or thrombin activatable fibrinolysis inhibitor (TAFI). The activation of the zymogen proceeds through a proteolytic cleavage at Arg-92. The active form - CPU - is able to retard the initial phase of fibrinolysis by cleaving C-terminal lysine residues exposed on fibrin partially degraded by the action of plasmin. These C-terminal lysine residues are essential for the high affinity binding of plasminogen to fibrin and the subsequent activation to plasmin. In this report, the activation of purified human proCPU was studied using trypsin and some key proteases of the coagulation and fibrinolytic cascade, i.e., kallikrein, plasmin and thrombin. The most efficient activation is obtained in the presence of thrombin in complex with thrombomodulin. After in vitro activation, CPU is unstable at 37 degrees C (T(1/2)=15 min). Its stability can be improved dramatically using lower temperatures.

A novel carboxypeptidase B that processes native beta-amyloid precursor protein is present in human hippocampus

The processing of beta-amyloid precursor protein (APP) and generation of beta-amyloid (Abeta) are associated with the pathophysiology of Alzheimer's disease (AD). As the proteases responsible for the process in the human brain have yet to be clarified, we have searched for activities capable of cleaving native brain APP in the human hippocampus. A 40-kDa protein with proteolytic activity that degrades native brain APP in vitro was purified and characterized; molecular analysis identified it as a novel protease belonging to the carboxypeptidase B (CPB) family. PC12 cells overexpressing the cDNA encoding this protease generate a major 12-kDa beta-amyloid-bearing peptide in cytosol, a peptide which has also been detected in a cell-free system using purified brain APP as substrate. Although the protease is homologous to plasma CPB synthesized in liver, it has specific domains such as C-terminal 14 amino acid residues. Western analysis, cDNA-cloning process and Northern analysis suggested a brain-specific expression of this protease. An immunohistochemical study showed that the protease is expressed in various neuronal perikarya, including those of pyramidal neurons of the hippocampus and ependymal-choroid plexus cells, and in a portion of the microglia of normal brains. In brains of patients with sporadic AD, there is decreased neuronal expression of the protease, and clusters of microglia with protease immunoreactivity associated with its extracellular deposition are detected. These findings suggest that brain CPB has a physiological function in APP processing and may have significance in AD pathophysiology.

PSMA mimotope isolated from phage displayed peptide library can induce PSMA specific immune response

Prostate-specific membrane antigen (PSMA) is a cell surface glycoprotein expressed predominantly in prostate secretory acinar epithelium and prostate cancer cells as well as in several extraprostatic tissues. Mouse monoclonal antibody 4G5 specific to the extracellular domain of PSMA was used to screen two phage displayed peptide libraries (9aa linear and 9aa cys library). Three 4G5-reactive phagotopes were identified. Sequence analysis of isolated clones demonstrated that the interaction motif "VDPA/SK" has high homology to 719-725aa on PSMA. Immunohistochemical staining of the prostate cancer sample with the PSMA-mimic phagotope (mimotope) immunized serum antibodies demonstrate that the mimotope isolated from the phage displayed peptide libraries can induce PSMA specific immune response in vivo.

Purification and some properties of camel carboxypeptidase B

A carboxypeptidase B-like enzyme was purified 116-fold with a recovery of activity of 29% from a crude extract of camel pancreas by a four-step procedure consisting of two anion exchange chromatographies in succession, gel filtration and hydrophobic interaction chromatography. The enzyme was homogeneous on SDS and non-denaturing gel electrophoresis and on gel isoelectric focusing. Its molecular mass was found to be 31.5 kDa and its isoelectric point was estimated as 6.1. It was active towards a number of substrates that are cleaved by carboxypeptidases B from other species and was also susceptible to inhibition by inhibitors of such enzymes. The camel enzyme showed a pH optimum of 8.0 and it was seen to be a relatively potent kininase in vitro. The enzyme purified in this study was very similar to carboxypeptidases B isolated from other species in size, charge, substrate specificity and susceptibility to inhibition and thus it can be identified as camel carboxypeptidase B.

Purification and characterization of a cobalt-activated carboxypeptidase from the hyperthermophilic archaeon Pyrococcus furiosus

A novel metallocarboxypeptidase (PfuCP) has been purified to homogeneity from the hyperthermophilic archaeon, Pyrococcus furiosus, with its intended use in C-terminal ladder sequencing of proteins and peptides at elevated temperatures. PfuCP was purified in its inactive state by the addition of ethylenediaminetetraacetic acid (EDTA) and dithiothreitol (DTT) to purification buffers, and the activity was restored by the addition of divalent cobalt (K, = 24 +/- 4 microM at 80 degrees C). The serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) had no effect on the activity. The molecular mass of monomeric PfuCP is 59 kDa as determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and 58 kDa by SDS-PAGE analysis. In solution, PfuCP exists as a homodimer of approximately 128 kDa as determined by gel filtration chromatography. The activity of PfuCP exhibits a temperature optimum exceeding 90 degrees C under ambient pressure, and a narrow pH optimum of 6.2-6.6. Addition of Co2+ to the apoPfuCP at room temperature does not alter its far-UV circular dichroism (CD) or its intrinsic fluorescence spectrum. Even when the CoPfuCP is heated to 80 degrees C, its far-UV CD shows a minimal change in the global conformation and the intrinsic fluorescence of aromatic residues shows only a partial quenching. Changes in the intrinsic fluorescence appear essentially reversible with temperature. Finally, the far-UV CD and intrinsic fluorescence data suggest that the overall structure of the holoenzyme is extremely thermostable. However, the activities of both the apo and holo enzyme exhibit a similar second-order decay over time, with 50% activity remaining after approximately 40 min at 80 degrees C. The N-blocked synthetic dipeptide, N-carbobenzoxy-Ala-Arg (ZAR), was used in the purification assay. The kinetic parameters at 80 degrees C with 0.4 mM CoCl2 were: Km, 0.9 +/- 0.1 mM; Vmax, 2,300 +/- 70 U mg(-1); and turn over number, 600 +/- 20 s(-1). Activity against other ZAX substrates (X = V, L, I, M, W, Y, F, N, A, S, H, K) revealed a broad specificity for neutral, aromatic, polar, and basic C-terminal residues. This broad specificity was confirmed by the C-terminal ladder sequencing of several synthetic and natural peptides, including porcine N-acetyl-renin substrate, for which we have observed (by MALDI-TOF MS) stepwise hydrolysis by PfuCP of up to seven residues from the C-terminus: Ac-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Leu-Val-Tyr-Ser.

Purification and properties of extracellular carboxyl proteases of acid-tolerant bacteria, isolated from compost

Four strains of acid-tolerant and protein-using bacteria were isolated from compost. Two of them, Gram-negative strains MB8 and MB11, were identified as a new genus close to Stenotrophomonas species MB8 and Burkholderia species MB11, respectively. Both bacteria produced extracellular carboxyl proteases (CP) in acid-casein-starch medium. The enzymes, termed CP MB8 and CP MB11, purified through ion exchange and gel filtration chromatographies had molecular weights of 61,000 (CP MB8) and 36,000 (CP MB11) as estimated by SDS-PAGE, and showed optimum activities with hemoglobin as a substrate at pH 3.5 (CP MB8) and pH 3.7 (CP MB11) at 55 degrees C. Both of the enzymes were not inhibited by pepstatin, DAN, or EPNP. These results suggest that both enzymes are members of the pepstatin-insensitive carboxyl proteinase family (EC 3.4.23.33), except for a larger molecular weight of the CP MB8 enzyme.

Carboxypeptidase M, a glycosylphosphatidylinositol-anchored protein, is localized on both the apical and basolateral domains of polarized Madin-Darby canine kidney cells

Carboxypeptidase M, a glycosylphosphatidylinositol-anchored membrane glycoprotein, is highly expressed in Madin-Darby canine kidney (MDCK) cells, where it was previously shown that the glycosylphosphatidylinositol anchor and N-linked carbohydrate are apical targeting signals. Here, we show that carboxypeptidase M has an unusual, non-polarized distribution, with up to 44% on the basolateral domain of polarized MDCK cells grown on semipermeable inserts. Alkaline phosphatase, as well as five other glycosylphosphatidylinositol-anchored proteins, and transmembrane gamma-glutamyl transpeptidase exhibited the expected apical localization. Basolateral carboxypeptidase M was readily released by exogenous phosphatidylinositol-specific phospholipase C, showing it is glycosylphosphatidylinositol-anchored, whereas apical carboxypeptidase M was more resistant to release. In contrast, the spontaneous release of carboxypeptidase M into the medium was much higher on the apical than the basolateral domain. In pulse-chase studies, newly synthesized carboxypeptidase M arrived in equal amounts within 30 min on both domains, indicating direct sorting. After 4-8 h of chase, the steady-state distribution was attained, possibly due to transcytosis from the basolateral to the apical domain. These data suggest the presence of a unique basolateral targeting signal in carboxypeptidase M that competes with its apical targeting signals, resulting in a non-polarized distribution in MDCK cells.

The membrane-bound basic carboxypeptidase from hog intestinal mucosa(1)

The carboxypeptidase activity occurring in hog intestinal mucosa is apparently due to two distinct enzymes which may be responsible for the release of basic COOH-terminal amino acids from short peptides. The plasma membrane-bound carboxypeptidase activity which occurs at neutral optimum pH levels was found to be enhanced by CoCl(2) and inhibited by guanidinoethylmercaptosuccinic acid, o-phenanthroline, ethylenediamine tetraacetic acid and cadmium acetate; whereas the soluble carboxypeptidase activity which occurs at an optimum pH level of 5.0 was not activated by CoCl(2) and only slightly inhibited by o-phenanthroline, ethylenediamine tetraacetic acid, NiCl(2) and CdCl(2). The latter activity was presumably due to lysosomal cathepsin B, which is known to be present in the soluble fraction of hog intestinal mucosa. Although the membrane-bound enzyme was evenly distributed along the small intestine, it was not anchored in the phospholipidic bilayer via a glycosyl-phosphatidylinositol moiety, as carboxypeptidase M from human placenta is. The enzyme was not solubilized by phosphatidylinositol-specific phospholipase C, but was solubilized to practically the same extent by several detergents. The purified trypsin-solubilized form is a glycoprotein with a molecular mass of 200 kDa, as determined by performing SDS-PAGE and gel filtration, which differs considerably from the molecular mass of human placental carboxypeptidase M (62 kDa). It was found to cleave lysyl bonds more rapidly than arginyl bonds, which is not so in the case of carboxypeptidase M, and immunoblotting analysis provided further evidence that hog intestinal and human placental membrane-bound carboxypeptidases do not bear much resemblance to each other. Since the latter enzyme has been called carboxypeptidase M, it is suggested that the former might be carboxypeptidase D, the recently described new member of the carboxypeptide B-type family.

Purification, characterization, and heterologous expression in Fusarium venenatum of a novel serine carboxypeptidase from Aspergillus oryzae

A novel serine carboxypeptidase (EC 3.4.16.1) was found in an Aspergillus oryzae fermentation broth and was purified to homogeneity. This enzyme has a molecular weight of ca. 67,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and its specific activity is 21 U/mg for carbobenzoxy (Z)-Ala-Glu at pH 4.5 and 25 degrees C. It has a ratio of bimolecular constants for Z-Ala-Lys and Z-Ala-Phe of 3.75. Optimal enzyme activity occurs at pH 4 to 4.5 and 58 to 60 degrees C for Z-Ala-Ile. The N terminus of this carboxypeptidase is blocked. Internal fragments, obtained by cyanogen bromide digestion, were sequenced. PCR primers were then made based on the peptide sequence information, and the full-length gene sequence was obtained. An expression vector that contained the recombinant carboxypeptidase gene was used to transform a Fusarium venenatum host strain. The transformed strain of F. venenatum expressed an active recombinant carboxypeptidase. In F. venenatum, the recombinant carboxypeptidase produced two bands which had molecular weights greater than the molecular weight of the native carboxypeptidase from A. oryzae. Although the molecular weights of the native and recombinant enzymes differ, these enzymes have very similar kinetic parameters.

Role of carbohydrate moiety in carboxypeptidase Y: structural study of mutant enzyme lacking carbohydrate moiety

To study the roles of the carbohydrate moiety in the function of carboxypeptidase Y, asparagine residues at 13, 87, 168, and 368, the four-consensus N-linked glycosylation sites, were altered to alanine with site-directed mutagenesis. The mutant enzyme of 51 kDa completely lost the carbohydrate moiety which was present in the 61-kDa wild-type enzyme. Structural studies of the mutant enzyme showed that it maintained the native-like structure; hydrolytic activity, and substrate specificity of the mutant enzyme analogous to those of the wild-type enzyme. Susceptibility of the mutant enzyme toward proteolysis and pressure denaturation was reduced by 10-20%. It is concluded that the carbohydrate moiety functions to maintain the structural integrity of the enzyme under stressed.

Characterization of the gene encoding human TAFI (thrombin-activable fibrinolysis inhibitor; plasma procarboxypeptidase B)

Thrombin-activable fibrinolysis inhibitor (TAFI) is a recently described human plasma zymogen that is related to pancreatic carboxypeptidase B. The active form of TAFI (TAFIa), which is formed by thrombin cleavage of the zymogen, likely inhibits fibrinolysis by removal from partially degraded fibrin of the carboxyl-terminal lysine residues which act to stimulate plasminogen activation. We have isolated and characterized genomic clones which encompass the entire human TAFI gene from lambda phage and bacterial artificial chromosome genomic libraries. The complete TAFI gene contains 11 exons and spans approximately 48 kb of genomic DNA. The positions of intron/exon boundaries are conserved between the TAFI gene and the rat pancreatic carboxypeptidase A1, A2, and B and the human mast cell carboxypeptidase A genes, indicating that these carboxypeptidases arose from a common ancestral gene. However, the intron lengths diverge significantly among all of these genes. The TAFI promoter lacks a consensus TATA sequence, and transcription is initiated from multiple sites. Transient transfection of reporter plasmids containing portions of the TAFI 5'-flanking region into mammalian cells allowed localization of the promoter and identified a approximately 70 bp region crucial for liver-specific transcription. Sequence analysis of cDNA clones obtained from human liver RNA indicated that the TAFI transcript is polyadenylated at three different sites. Our findings will facilitate the assessment of the regulation of TAFI expression by transcriptional and/or posttranscriptional mechanisms. Furthermore, knowledge of the genomic structure of the TAFI gene will aid in the identification of mutations that may be associated with the tendency to either bleed or thrombose.

Purification, cDNA cloning, and expression of a new human blood plasma glutamate carboxypeptidase homologous to N-acetyl-aspartyl-alpha-glutamate carboxypeptidase/prostate-specific membrane antigen

We describe the identification, cDNA cloning, and biochemical characterization of a new human blood plasma glutamate carboxypeptidase (PGCP). PGCP was co-purified from human placenta with lysosomal carboxypeptidase, cathepsin A, lysosomal endopeptidase, cathepsin D, and a gamma-interferon-inducible protein, IP-30, using an affinity chromatography on a Phe-Leu-agarose column. A PGCP cDNA was obtained as an expressed sequence tag clone and completed at 5'-end by rapid amplification of cDNA ends polymerase chain reaction. The cDNA contained a 1623-base pair open reading frame predicting a 541-amino acid protein, with five putative Asn glycosylation sites and a 21-residue signal peptide. PGCP showed significant amino acid sequence homology to several cocatalytic metallopeptidases including a glutamate carboxypeptidase II also known as N-acetyl-aspartyl-alpha-glutamate carboxypeptidase or as prostate-specific membrane antigen and expressed glutamate carboxypeptidase activity. Expression of the PGCP cDNA in COS-1 cells, followed by Western blotting and metabolic labeling showed that PGCP is synthesized as a 62-kDa precursor, which is processed to a 56-kDa mature form containing two Asn-linked oligosaccharide chains. The mature form of PGCP was secreted into the culture medium, which is consistent with its intracellular localization in secretion granules. In humans, PGCP is found principally in blood plasma, suggesting a potential role in the metabolism of secreted peptides.

Purification and characterization of human metallocarboxypeptidase Z

Carboxypeptidase Z (CPZ) is a recently discovered member of the metallocarboxypeptidase gene family that has an N-terminal domain related to the Wnt/wingless binding domain of frizzled receptors and other proteins. To further characterize the enzymatic properties of CPZ, the enzyme was purified using Arg- and heparin-affinity columns. CPZ has a neutral pH optimum, and is inhibited by chelating agents and several divalent cations (Zn2+, Mn2+, Cd2+, Cu2+, Hg2+). Active site-directed inhibitors of several other metallocarboxypeptidases also inhibit CPZ activity with moderate potency. CPZ cleaves substrates with C-terminal Arg residues, preferring peptides with an Ala in the penultimate position. No activity is detected toward substrates with an Ile-Arg or a Pro-Arg sequence. The Km for dansyl-Phe-Ala-Arg and dansyl-Pro-Ala-Arg are both approximately 2 mM. Taken together, these data suggests a selective role for CPZ in the processing of extracellular peptides or proteins.

A soluble form of the avian hepatitis B virus receptor. Biochemical characterization and functional analysis of the receptor ligand complex

Avian hepatitis B virus infection is initiated by the specific interaction of the extracellular preS part of the large viral envelope protein with carboxypeptidase D (gp180), the primary cellular receptor. To functionally and biochemically characterize this interaction, we purified a soluble form of duck carboxypeptidase D from a baculovirus expression system, confirmed its receptor function, and investigated the contribution of different preS sequence elements to receptor binding by surface plasmon resonance analysis. We found that preS binds duck carboxypeptidase D with a 1:1 stoichiometry, thereby inducing conformational changes but not oligomerization. The association constant of the complex was determined to be 2.2 x 10(7) M-1 at 37 degreesC, pH 7.4, with an association rate of 4.0 x 10(4) M-1 s-1 and a dissociation rate of 1.9 x 10(-3) s-1, substantiating high affinity interaction of avihepadnaviruses with their receptor carboxypeptidase D. The separately expressed receptor-binding domain, comprising about 50% of preS as defined by mutational analysis, exhibits similar constants. The domain consists of an essential element, probably responsible for the initial receptor contact and a part that contributes to complex stabilization in a conformation sensitive manner. Together with previous results from cell biological studies these data provide new insights into the initial step of hepadnaviral infection.

The isolation and partial characterization of precursor forms of ostrich carboxypeptidase

Ostrich carboxypeptidases A and B were recently purified and characterized. The aim of this study was to isolate and purify, and partially characterize in terms of molecular weight, pI, amino acid composition and N-terminal sequencing, the precursor forms of carboxypeptidases from the ostrich pancreas. Inhibition studies with soybean trypsin inhibitor and activation studies with three proteases (bovine trypsin, bovine chymotrypsin and porcine elastase) were performed on crude ostrich acetone powder and the carboxypeptidase A and B activities were determined. SDS-PAGE was carried out after every incubation to monitor the rate and degree of conversion of a M(r) 66K component to procarboxypeptidase and carboxypeptidase A and B. The precursor forms were purified by Toyopearl Super Q and Pharmacia Mono Q chromatography. All three proteases converted the M(r) 66K component to procarboxypeptidases and carboxypeptidases over a set time interval, with carboxypeptidase A and B activities being detected in the acetone powder. Chymotrypsin was the preferred protease since it exhibited a more controlled activation of the procarboxypeptidases. The amino acid composition of procarboxypeptidase A revealed 525 residues. The N-terminal sequence of procarboxypeptidase A showed considerable homology when compared with several other mammalian sequences. M(r) and pI values of 52K and 5.23 were obtained for procarboxypeptidase A, respectively. This study indicated that ostrich procarboxypeptidase A is closely related to other mammalian procarboxypeptidase A molecules in terms of physicochemical properties.