Structurally dissimilar proteins with antiviral and antifungal potency from cowpea (Vigna unguiculata) seeds

Abstract

Evidence is presented for the existence of multiple proteins with antifungal and antiviral potency in cowpea seeds. The two proteins, designated alpha- and beta-antifungal proteins in accordance with their order of elution from the CM-Sepharose column, were capable of inhibiting human immunodeficiency virus (HIV) reverse transcriptase and one of the glycohydrolases associated with HIV infection, alpha-glucosidase, but beta-glucuronidase was not repressed. The ability of the proteins in retarding mycelial growth of a variety of fungi was also demonstrated with alpha-antifungal protein being more potent in most of the cases. Beta-antifungal protein was more active in only one instance. Both antifungal proteins had low cell-free translation-inhibitory activity. The proteins were adsorbed on Affi-gel blue gel-and CM-Sepharose but could be separated from one another during chromatography on the latter medium by means of a linear NaCl concentration gradient. Different molecular weights were exhibited by the proteins, being 28 kDa and 12 kDa respectively for alpha- and beta- antifungal proteins. Alpha-antifungal protein was characterized by an N-terminal sequence showing close resemblance to sequences of chitinases. Beta-antifungal protein exhibited an N-terminal sequence hitherto unknown in the literature.