X-Ray Crystallographic Study of a Non-Pepsin-Type Acid Proteinase, Aspergillus Niger Proteinase A

Abstract

Acid proteinase A, secreted by the fungus Aspergillus niger var. macrosporus, is a non-pepsin-type acid proteinase as judged from its distinct differences in various properties from the ordinary pepsin-type aspartic proteinase family [1,2]. It is insensitive to pepstatin, diazoacetyl-DL-norleucine methyl ester (DAN), and l,2-epoxy-3-(p-nitrophenoxy)propane (EPNP) [3], and shows fairly different substrate specificity [4]. The enzyme is composed of two chains, and the relative molecular mass is 22,300, about half the size of the ordinary pepsin-type proteinases. No protein in the GenBank database is homologous in the primary structure with proteinase A except for Scytalidium lignicolum proteinase B [5] that shows about 50% identity [2]. Proteinase A has no consensus sequence, Asp-Thr/Ser-Gly, including the catalytic aspartic acid residue, present in the family of pepsin-type proteinases. It, thus, remains to be elucidated which residues participate in the catalysis and how the mechanism operates. Moreover, it is of interest to elucidate how the three-dimensional structure differs from pepsin-type enzymes. Comparison of the crystal structure of proteinase A with those of pepsin-type enzymes will enable us to explain the unusual properties of this enzyme. To approach these queries, we have started the crystallographic study of the enzyme, and have obtained an isomorphous heavy atom derivative of the crystals.KeywordsAspergillus NigerHigh Energy PhysicsAspartic ProteinaseAcid ProteinasePhoton FactoryThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.