| Research Abstract |
It is well known that carboxyl proteases are commonly inhibited by pepstatin^<1)>, DAN^<2)> and EPNP^<3)>, and their catalytic residues are composed of two aspartic acid residues. Thus, carboxyl proteases are termed aspartic proteases. These enzymes are highly homologous in both the primary and tertiary structures.
We have isolated novel carboxyl proteases from fungi, bacteria and also thermophilic bacteria based on their insensitivities to pepstatin, DAN and EPNP. These enzymes were tentatively named pepstatin-insensitve carboxyl proteases. In one of our studies, the primary structure of carboxyl protease B(consisting of 204 amino acids)from a fungus Scytalidium lignicolum has been established, one of the catalytic residues of which was clarified to be Glu-53. This is the first report on glutamic protease. It seemed probable that the pepstatin-insensitive carboxyl proteases are not aspartic proteases but glutamic proteases. To confirm this possibility, we focussed our studies on a peps
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tatin-insensitive carboxyl protease from Pseudonionas sp. No. 101(PCP), which is the the first carboxyl protease-isolated from prokaryote cells. The primary structure of PCP has been determined to be a single polypeptide composed of 372 amino acid residues with one disulfide bridge. PCP does not have any homologous structure to those of aspartic proteases reported so far. Moreover, the well-conserved structure, -Asp*-Thr-Gly- in the active center of aspartic proteases was not observed.
In this study, the following results were obtained.
1. Identification of Catalytic Residues In our attempt to use inhibitor in the study of active center, we had isolated a novel inhibitor, tyrostatin(N-isovaleryl-tyrosyl-leucyl-tyrosinal, Ki = 2.5 nM)from Kitasatosporia sp. No. 55. Based on the chemical structure, we succeeded in synthesizing a competitive inhibitor, available for probing the catalytic residues of PCP(Carbobenzoxy-Tyr-O-CH_2-Epoxide).
2. Analysis of PCP Gene We determined the whole DNA sequence of the PCP gene(abaout 3 kbp). it was elucidated that PCP is composed of prepro part protein(215 amino acid residues)and mature protein(372 amino acid residues). Primary structure of the mature protein was identical to that chemically determined previously. It was suggested that the propart protein plays important roles in the activation as well as secretion through the double layer of the cell.
Accordingly, it is ready now to study the structure-function relationships, especially the catalytic residues on both side of protein and DNA level.
1)pepstatin, pepsin inhibitor ; 2)DAN, diazoacetyl-DL-norleucine methylester ; 3)EPNP, 1.2-epoxy-3(P-nitrophenoxy)propane. Less
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