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We have recently shown that crude Trimeresurus flavoviridis (habu snake) venom has a strong capability for activating the human alternative complement system. To identify the active component, the crude venom was fractionated and purified by serial chromatography using Sephadex G-100, CM-cellulose C-52, diethylaminoethyl-Toyopearl 650M, and Butyl-Toyopearl, and the active fractions were evaluated by the C3a-releasing and soluble membrane attack complex-forming activities. Two peak fractions with the highest activities were detected after gel filtration and ion exchange chromatography, and the first fraction was purified to homogeneity. The homogeneous protein was examined for its N-terminal amino acid sequence by Edman degradation. The determined sequence of 25 amino acids completely coincided with that of a previously reported serine protease with coagulant activity, flavoxobin, purified from the same snake venom. To elucidate the molecular mechanism of the complement activation, the reactive products of the mixture of the purified human C3 and flavoxobin were examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The digesting pattern revealed that flavoxobin cleaves the alpha chain of the C3 molecule into two fragments. The N-terminal amino acid sequences for the remnant fragments of C3 disclosed that flavoxobin severs the human C3 at the Arg726-Ser727 site to form C3b and C3a the way C3bBb, the human alternative C3 convertase, does. In conclusion, flavoxobin acts as a novel, heterologous C3 convertase that independently cleaves human C3 and kick-starts the complement cascade.

A strain of Aeromonas hydrophila was found to show prolyl endopeptidase activity. The enzyme gene was cloned and expressed in Escherichia coli JM83. A 12 kbp EcoRI fragment containing the enzyme gene was subcloned at the HincII site of pUC19 to construct plasmid pAPEP-3 with a 3.5 kbp insert. E. coli JM83 transformed with this plasmid showed about 100-fold higher activity than the parent Aeromonas. Analysis of the nucleotide sequence of the insert revealed that the mature enzyme-encoding sequence starts just after the ATG initiation codon of the open reading frame. The enzyme was a single polypeptide composed of 689 amino acid residues with a molecular weight of 76,383. It showed properties very similar to those of Flavobacterium prolyl endopeptidase, except that the isoelectric point was 5.5. The amino acid sequence was 56 and 41% homologous to those of Flavobacterium and porcine brain prolyl endopeptidases, respectively. From a survey of sequence homology with other members of the prolyl endopeptidase family, the amino acid residues involved in the catalytic triad were deduced to be Ser-537, His-656, and Asp-512 (or Asp-621).

The prolyl endopeptidase [EC 3.4.21.26] gene of Flavobacterium meningosepticum was cloned in Escherichia coli with the aid of an oligonucleotide probe which was prepared based on the amino acid sequence. The hybrid plasmid, pFPEP1, with a 3.5 kbp insert at the HincII site of pUC19 containing the enzyme gene, was subcloned into pUC19 to construct plasmid pFPEP3. The whole nucleotide sequence of an inserted HincII-BamHI fragment of plasmid pFPEP3 was determined by the dideoxy chain-terminating method. The purified prolyl endopeptidase was labeled with tritium DFP, and the sequence surrounding the reactive serine residue was found to be Ala (551)-Leu-Ser-Gly-Arg-*Ser-Asn(557). Ser-556 was identified as a reactive serine residue. The enzyme consists of 705 amino acid residues as deduced from the nucleotide sequence and has a molecular weight of 78,705, which coincides well with the value estimated by ultra centrifugal analysis. The amino acid sequence was 38.2% homologous to that of the porcine brain prolyl endopeptidase [Rennex et al. (1991) Biochemistry 30, 2195-2203] and 24.5% homologous to E. coli protease II, which has substrate specificity for basic amino acids [Kanatani et al. (1991) J. Biochem. 110, 315-320].

Protease II gene of Escherichia coli HB101 was cloned and expressed in E. coli JM83. The transformant harboring a hybrid plasmid, pPROII-12, with a 2.4 kbp fragment showed 90-fold higher enzyme activity than the host. The whole nucleotide sequence of the inserted fragment of plasmid pPROII-12 was clarified by the dideoxy chain-terminating method. The sequence that encoded the mature enzyme protein was found to start at an ATG codon, as judged by comparison with amino terminal protein sequencing. The molecular weight of the enzyme was estimated to be 81,858 from the nucleotide sequence. The reactive serine residue of protease II was identified as Ser-532 with tritium DFP. The sequence around the serine residue is coincident with the common sequence of Gly-X-Ser-X-Gly, which has been found in the active site of serine proteases. Except for this region, protease II showed no significant sequence homology with E. coli serine proteases, protease IV and protease La (lon gene), or other known families of serine proteases. However, 25.3% homology was observed between protease II and prolyl endopeptidase from porcine brain. Although the substrate specificities of these two enzymes are quite different, it seems possible to classify protease II as a member of the prolyl endopeptidase family from the structural point of view.

Structural requirements of N-blocked L-proline derivatives as specific inhibitors for prolyl endopeptidase were investigated using a series of substrate analogs. Replacement of L-proline by its D-isomer remarkably reduced the inhibition. Introduction of a sulfur atom in proline and/or in the penultimate pyrrolidine rings significantly increased the inhibition, but the introduction of oxygen rather diminished the activity. A peptide linkage (acid-amide bond) between the proline and the pyrrolidine ring was also required to keep the inhibitory activity. A benzyloxycarbonyl group was most effective as an N-blocked component of the inhibitors.

Prolyl endopeptidase [EC 3.4.21.26] was purified to homogeneity from the culture filtrate of Agaricus bisporus by a procedure that comprised ammonium sulfate fractionation, anion-exchange chromatographies on DEAE-Toyopearl and DEAE-Sephadex, hydroxylapatite chromatography, and high-performance liquid chromatography (HPLC) on a TSKgel G 2000 SW column. The overall activity recovery was 8.6%. The enzyme was most active at or around pH 7.5 and was stable in the range of pH 5-9 when checked with Z-Gly-Pro-beta-naphthylamide as a substrate. The isoelectric point of the enzyme was about 4.8. The enzyme was a monomeric protein of molecular weight 78,000 +/- 2,000 as judged by gel permeation chromatography on Sephadex G-150 and electrophoresis on sodium dodecyl sulfate (SDS) polyacrylamide gel. The enzyme hydrolyzed Pro-X bonds and at least five subsites (S3, S2, S1, S1', and S2') were found to be involved in enzyme-substrate binding. Among them, S2, S1, and S1' subsites of the enzyme showed high stereospecificity. The enzyme was strongly inhibited by diisopropylfluorophosphate (DFP), Z-Gly-Pro-CH2Cl, Z-Pro-prolinal, Z-Pro-pyrrolidine, Z-Thiopro-pyrrolidine, Z-Pro-thiazolidine, Z-Thioprothiazolidine, and p-chloromercuribenzoate (PCMB), while it was not inhibited by phenyl-methylsulfonyl fluoride (PMSF), E-64, iodoacetamide, or metal chelators. Although the A. bisporus enzyme showed no immunological cross reaction with anti-bovine prolyl endopeptidase antiserum, the other characteristics were quite similar to those of mammalian and plant enzymes.

High prolyl endopeptidase (post-proline cleaving enzyme) [EC 3.4.21.26] activity was detected in fruit bodies of shakashimeji (Lyophyllum cinerascens), tsukuritake (mushroom: Agaricus bisporus), hirohachichitake (Lactarius hygrophoroides), and yaburebenitake (Russula lepida) which belong to the genus Basidiomycetes. Cell-free extract of shakashimeji showed high activities of proline iminopeptidase and arylamidase as well as prolyl endopeptidase. The prolyl endopeptidase was purified from the extract of shakashimeji by sequential chromatographies on DEAE-Toyopearl, DEAE-Sephadex and hydroxyapatite, and high-performance liquid chromatography with a DEAE-5PW column. The purified enzyme was homogeneous as judged by disc gel electrophoresis. The enzyme was most active at pH 6.8 as checked with Z-Gly-Pro-beta-naphthylamide as a substrate and was stable in the range of pH 5.8-7.4. The isoelectric point of the enzyme was 5.2 and the molecular weight was estimated to be 76,000 by gel filtration on Sephadex G-150 and by sodium dodecyl sulfate (SDS) gel electrophoresis, suggesting that the enzyme was a monomer. The enzyme was completely inhibited by diisopropyl fluorophosphate (DFP), Z-Gly-Pro-CH2Cl, and Z-Pro-prolinal, while it was not inhibited by p-chloromercuribenzoate (PCMB), phenylmethylsulfonyl fluoride (PMSF), or metal chelators. It was estimated that at least five subsites were concerned with the enzyme-substrate binding. Among them, the S1, S2, and S1' sites showed high stereospecificity, as in mammalian, microbial, and plant enzymes. The enzyme hydrolyzed TRH at the carboxyl side of the proline residue. The mushroom enzyme, that was sensitive to DFP, Z-Pro-prolinal, and Z-Gly-Pro-CH2Cl, but not to PCMB, were quite similar in characteristics to the Flavobacterium enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

An inhibitor(s) for post-proline cleaving enzyme was checked by using a fluorogenic substrate, Z-Gly-Pro-4-methyl coumarinamide, and was found to be distributed widely in rat and porcine organs. The highest inhibitory activity on the enzyme was observed in pancreas and the inhibitor was partially purified from porcine pancreas extract by heat treatment, chromatographies on DEAE-Sephadex and Sephadex G-50 and affinity chromatography on trypsin-Sepharose. This inhibitor was very stable against temperature, pH and trichloroacetic acid treatment. The molecular weight was estimated to be 6500 by gel filtration. This inhibitor was highly specific for prolyl endopeptidases from mammals and Flavobacterium and inhibited the enzyme competitively. It acted neither on proline specific exopeptidases such as dipeptidyl aminopeptidase IV, proline aminopeptidase, prolidase, nor usual endopeptidases such as trypsin and alpha-chymotrypsin.

The gene encoding subtilisin Amylosacchariticus from Bacillus subtilis var. amylosacchariticus was isolated and the entire nucleotide sequence of the coding sequence was determined. The deduced amino acid sequence revealed an N-terminal signal peptide and pro-peptide of 106 residues followed by the mature protein comprising 275 residues. There were discrepancies in 10 amino acids between the sequence elucidated from the nucleotide sequence and the published protein sequence (Kurihara et al. (1972) J. Biol. Chem. 247, 5619-5631). The nucleotide sequence was highly homologous to that of subtilisin E gene from B. subtilis 168, with discrepancies at 12 nucleotides out of 1,426 nucleotides we sequenced. Ten of them were found in mature subtilisin coding sequence, which resulted in two amino acid changes and another one was in the putative promoter region between two genes. The productivity of subtilisin in culture broth of B. subtilis var. amylosacchariticus was much higher than that of B. subtilis 168. The enzyme gene was inserted in a shuttle vector pHY300PLK, with which B. subtilis ISW1214 was transformed. The proteolytic activity found in the culture broth of the transformed bacterium was 20- and 4-fold higher than those of the host strain and B. subtilis var. amylosacchariticus, respectively. Subtilisin Amylosacchariticus was easily purified to a crystalline form from culture filtrate of cloned B. subtilis, after a single step of chromatography on CM-cellulose.

A post-proline cleaving enzyme [prolyl endopeptidase, EC 3.4.21.26] was purified about 3,700-fold from an extract of bovine brain by a series of column chromatographies on DEAE-Sephadex, hydroxyapatite and PCMB-T-Sepharose, and gel filtration on Sephadex G-200 using N-carbobenzoxy-Gly-Pro-beta-naphthylamide (Z-Gly-Pro-2-NNap), thyrotropin releasing hormone (TRH) and oxytocin as substrates. The purified enzyme appeared homogeneous as judged by disc gel and SDS gel electrophoreses. The enzyme was most active at pH 7.5 and 7.2 with Z-Gly-Pro-2-NNap and TRH, respectively, and hydrolyzed peptide bonds involving Pro-X (X=amino acid, peptide, ester and amide) bonds of synthetic substrates, oxytocin, vasopressin, neurotensin, substance P, tuftsin, bradykinin, and insulin B chain. However, the enzyme was inert toward collagen, gelatin, and casein. The enzyme was completely inactivated by diisopropylphosphorofluoridate (DFP), Z-Gly-Pro-chloromethyl ketone and p-chloromercuribenzoate (PCMB), while it was not inhibited by phenylmethane sulfonylfluoride (PMSF) or metal chelators. Determination of the amino acid composition revealed that the enzyme contained 25 half-cystines. Modification of three cysteine residues of the enzyme by PCMB led to complete inactivation. The isoelectric point of the enzyme was 4.8, and the molecular weight was estimated to be 76,000 by ultracentrifugal analysis and 75,000-74,000 by both gel filtration and sodium dodecyl sulfate (SDS) gel electrophoresis, suggesting that the enzyme is present as a monomer. These results indicate that the post-proline cleaving enzyme from bovine brain is very similar to those previously purified from lamb brain and kidney in its enzymatic properties, substrate specificity and physicochemical properties, in sharp contrast with the results obtained by Tate, who reported that the bovine brain prolyl endopeptidase was inert toward oxytocin, vasopressin and bradykinin.

The inhibitory effects of proline-containing peptides and their derivatives on prolyl endopeptidases from Flavobacterium meningosepticum and bovine brain were compared. Replacement of the carboxyl terminal proline in N-blocked peptides with prolinal resulted in remarkable decreases in Ki values for both prolyl endopeptidases. Further reduction of the prolinal to prolinol led to a decrease in their inhibitory effects. Z-Pro-, Z-Val-, and Suc-Pro-prolinals were similarly inhibitory for both the enzymes with Ki values of nM order. However, the inhibitory effects of Z-Pyr-prolinal and Boc-Pro-prolinal on these enzymes were significantly distinguished: they strongly inhibited the mammalian prolyl endopeptidase with Ki values of nM order, while the Ki values of these compounds for the microbial enzyme were only of microM order. These results suggest that there are some structural differences in the S2 and S3 subsites between the two enzymes, though their substrate specificities are apparently indistinguishable.

The substrate specificity of dipeptidyl peptidase IV (dipeptidyl peptide hydrolase, EC 3.4.14.5) from pig kidney and proline-specific endopeptidase from Flavobacterium meningosepticum, was investigated with a series of N-terminal unprotected (dipeptidyl peptidases IV) and succinylated dipeptidyl-p-nitroanilides (proline-specific endopeptidase). Both enzymes are specific for the S configuration of the amino-acid residue in P1 and P2 position if the penultimate residue is proline. In the case of alanine substrates (Ala in P1, dipeptidyl peptidase IV hydrolyzes such compounds where the configuration of the P2 residue is R. The penultimate residue with dipeptidyl peptidase IV can be, beside proline and alanine, dehydroproline, hydroxyproline and pipecolic acid. Proline substrates (Pro in P1) with an R configuration in P2 are inhibitors of the hydrolysis of proline substrates with an S,S configuration in an uncompetitive (dipeptidyl peptide IV) or mixed inhibition type (proline-specific endopeptidase). Derivatives of Gly-Pro-pNA where the N-terminal amino group is methylated are hydrolyzed by dipeptidyl peptidase IV.

A series of N-blocked L-proline-containing compounds and their derivatives were synthesized. Their inhibitory activities for prolyl endopeptidase from bovine brain were examined and compared with that of N-benzyloxycarbonyl-L-prolyl-L-prolinal, which is the most effective enzyme inhibitor hitherto reported. Introduction of a sulfur atom into pyrrolidine ring quite effectively increased the inhibitory activity: replacement of pyrrolidine with thiazolidine or thiazolidine aldehyde (thioprolinal) and conversion of L-proline to L-thioproline residue resulted in increase in the inhibitory activity. Thus, N-benzyloxycarbonyl-L-thioprolyl-thiazolidine (Z-Thiopro-thiazolidine) and Z-L-Thiopro-L-thioprolinal showed Ki values of 0.36 and 0.01 nM, respectively, for prolyl endopeptidase from bovine brain; both values were significantly lower than that of Z-Pro-prolinal (Ki, 3.7 nM).

A post-proline cleaving enzyme [post-proline endopeptidase: EC 3.4.21.26] was purified from lamb brain by a series of column chromatographies on DEAE-Sephadex, hydroxyapatite and Sephadex G-150. The purified enzyme appeared homogeneous on disc gel and sodium dodecyl sulfate (SDS) gel electrophoreses. The enzyme was most active at pH 7.0 with carbobenzoxy-Gly-Pro-beta-naphthylamide (Z-Gly-Pro-2-NNap) as a substrate and catalyzed the hydrolysis of oxytocin, vasopressin, thyrotropin releasing hormone (TRH), substance P, luteinizing hormone releasing hormone (LH-RH), and angiotensin at the carboxyl side of their proline residues, except for the Pro2-Lys3 bond in substance P. From the results of subsite mapping using synthetic peptides, five subsites, S3 to S2', for substrate interaction with the enzyme were deduced to be present, and high stereospecificity was observed at S2, S1, and S1'. The isoelectric point of the enzyme was at pH 4.9, and the molecular weights estimated by gel filtration and SDS gel electrophoresis were 74,000 and 77,000, respectively. The enzyme was markedly inhibited by diisopropylphosphoro fluoridate (DFP), carbobenzoxy-Gly-Pro-chloromethyl ketone (Z-Gly-Pro-CH2Cl), p-chloromercuribenzoate (PCMB), Hg2+, and Cu2+ ions. These enzymatic and protein chemical properties of post-proline cleaving enzyme from lamb brain closely resemble those of the lamb kidney enzyme, except for the molecular weight. In the present work, however, we decided that the molecular weight of the enzyme from lamb kidney was also 74,000, which is different from that reported previously (J. Biol. Chem. 251, 7593 (1976) but is in accord with the value of post-proline cleaving enzyme from lamb brain.

16 substrates of the types succinyl-alanyl-alanine-pX-anilide, and succinyl-alanyl-proline-pX anilide having different substituents in para-position of the aryl residue were synthesized and characterized. The influence of electronic as well as hydrophobic substituent constants, sigma and pi, on the hydrolysis of the substrates catalyzed by the enzyme Proline Specific Endopeptidase (PSE) has been investigated. In the Hansch approach, the catalytic constants lg kcat and lg (kcat/KM) of succinyl-alanyl-alanine-pX-anilides hydrolyzed by PSE correlate significantly with electronic substituent constants sigma, whereas no correlation in the case of succinyl-alanyl-proline-pX-anilides. The intercorrelation of the constants of the former substrates with corresponding data from Dipeptidyl Peptidase IV (DP IV) catalyzed hydrolysis of alanyl-alanine-pX-anilides suggest that both enzymes act by similar catalytic mechanism.