Dipeptidyl peptidases III (DPPIII) are zinc-dependent peptidases and constitute the M49 family of metalloproteases. These enzymes are presumed to play a general role in peptide catabolism in the cell cytoplasm and may also have more specific roles in mammalian physiology. Here, we describe the recombinant production and characterization of DPPIII from the ringless honey mushroom Armillariella tabescens (ArtaDPPIII). The purified protein possessed all characteristic features expected of an enzyme of the M49 family, such as cleavage of dipeptidyl-2-naphthylamides and inhibition by the peptide tynorphin. Previous reports that the enzyme is capable of oxidizing aflatoxin B1 and thus acts as a detoxifying enzyme could not be reproduced. In accordance with its enzymatic properties, the amino acid sequence of ArtaDPPIII exhibits all characteristics established for this protein family and lacks any features that could rationalize additional enzymatic activities, such as the putative aflatoxin oxidase activity. Thus, in conclusion, ArtaDPPIII is a canonical member of the M49 family of metalloproteases and earlier claims that the enzyme carries novel and very unusual oxidative activities are not supported by our study.
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