Fungal membrane responses induced by plant defensins and thionins

Treatment of hyphae of Neurospora crassa with antifungal plant defensins, i.e. Rs-AFP2 and Dm-AMP1 isolated from radish and dahlia seed, respectively, induced a rapid K+ efflux, Ca2+ uptake, and alkalinization of the incubation medium. The Rs-AFP2-induced alkalinization of the incubation medium could be inhibited with G-protein inhibitors. alpha-Hordothionin, an antifungal thionin from barley seed, caused a sustained increased Ca2+ uptake at subinhibitory concentrations but only a transient increased uptake at inhibitory concentrations. alpha-Hordothionin also caused increased K+ efflux and alkalinization of the medium, but these fluxes occurred more rapidly compared to those caused by plant defensins. Furthermore, alpha-hordothionin caused permeabilization of fungal hyphae to the non-metabolite alpha-aminoisobutyric acid and, in addition, altered the electrical properties of artificial lipid bilayers, consistently leading to rupture of the lipid bilayers. The plant defensins did not form ion-permeable pores in artificial membranes and did not exhibit substantial hyphal membrane permeabilization activity. Our results are consistent with the notion that thionins inhibit fungal growth as a result of direct protein-membrane interactions, whereas plant defensins might act via a different, possibly receptor-mediated, mechanism.     

A gene apparently determining the extent of sialylation of lysosomal alpha-mannosidase in mouse liver

Organ-specific electrophoretic heterogeneity of lysosomal alpha-mannosidase has been observed within individual strains of inbred mice. Polymorphism between C57BL/6J and CBA/J for liver lysosomal alpha-mannosidase is determined by a single genetic locus on chromosome 5 and appears to be the result of differences in sialylation of the lysosomal enzyme. Two different patterns of expression of development of the liver electrophoretic forms have been observed.     

Identification of alpha-dystroglycan as a receptor for lymphocytic choriomeningitis virus and Lassa fever virus

A peripheral membrane protein that is interactive with lymphocytic choriomeningitis virus (LCMV) was purified from cells permissive to infection. Tryptic peptides from this protein were determined to be alpha-dystroglycan (alpha-DG). Several strains of LCMV and other arenaviruses, including Lassa fever virus (LFV), Oliveros, and Mobala, bound to purified alpha-DG protein. Soluble alpha-DG blocked both LCMV and LFV infection. Cells bearing a null mutation of the gene encoding DG were resistant to LCMV infection, and reconstitution of DG expression in null mutant cells restored susceptibility to LCMV infection. Thus, alpha-DG is a cellular receptor for both LCMV and LFV.