| Research Abstract |
In this study, we aimed to identify the catalytic residues of pepstatin-insensitive carboxylproteinases from prokaryote cells. We focused our studies on carboxyl proteinases from Pseudomonas sp. 101 (PCP). Xanthomonas sp. T-22 (XCP), Bacillus coagulans J-4 (J-4), and Bacillus novosp. MN-32 (kumamolysin). The primary structures of them does not have any similarities to those of aspartic proteinases (pepstatin-insensitive carboxyl proteinase) reported so far. Moreover, the well-conserved structure, -Asp*-Thr-Gly-(Asp* : catalytic residue) in the active center of aspartic proteinases was not observed, The following results were obtained.
1. Identification of Catalytic Residues by Using Site-directed Mutagenesis Technique
PCP (372 amino acid residues) and XCP (398 amino acid residues) have 52% identity to each other. Based on the high sequence identity, eight amino acid residues for catalytic residues (Asp or Glu) were poked up, and all of them were mutated to Ala residues. We analyzed these
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Ala mutants for both auto-catalytic processing ability and proteinase activity. Consequently, a pair of Dl70 and D328 for PCP.And a pair of D169 and D348 for XCP were identified as catalytic residues, respectively.
2. Identification of Catalytic Residues by Using [14C] Stylene Oxide
In order to identify the catalytic residue(s) of XCP.[14C]stylene oxide was used. It was found that the [14C]stylene oxide was bound to E75 and D110 residues of XCP, respectively. Of them, E75 residue (corresponding to E80 residue of PCP) and its vicinities were conserved in PCP.Based on these data. E80 residue of PCP and E75 residue of XCP were thought to be involved in their catalytic function, as a substrate binding site, respectively.
3. Identification of Catalytic Residues by Using [14C] DCCD
In order to identify the catalytic residue(s) of PCP, chemical modification was carried out by using N.N'-dicyclohexylcarbodiimide (DCCD) and specific inhibitor, tyrostatin. It was found that [14C] DCCD was bound to D140 and E222 residues of PCP, respectively. Of them, E222 residue (corresponding to E235 residue of XCP) and its vicinities were found out to be conserved in XCP.Furthermore, E222A mutant had no any activity, whereas XE235A (corresponding to E222A for PCP) had proteinase activity. Based on these data. E222 residue of PCP and E235 of XCP were thought to be involved in their catalytic function. probably as a substrate binding site, respectively.
4. Cloning of Carboxyl Proteinase J-4 Gene from Bacillus coagulans
Bacilluscoagulans J-4 carboxyl proteinase. designated as J-4, is characterized as alcohol resistant and insensitive to pepstatin. Most of the gene has been cloned, sequenced. After getting the whole gene. we will try to construct a high expression system and determine the catalytic residues by site-directed mutagenesis.
5. Construction of High Expression System of Kumamolysin
Bacillus novosp. MN-32 carboxyl proteinase. designated as Kumamolysin. is characterized as thermostable enzyme. We succeeded in constructing the high expression system for this enzyme. Less
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