A Corn Trypsin Inhibitor with Antifungal Activity Inhibits Aspergillus flavus alpha-Amylase

A new peptidic protease inhibitor from Vicia faba seeds exhibits antifungal, HIV-1 reverse transcriptase inhibiting and mitogenic activities

A new trypsin-chymotrypsin Inhibitor, with an N-terminal sequence showing some differences from the previously reported trypsin-chymotrypsin inhibitor, was isolated from the broad bean Vicia faba. The inhibitor was a peptide with a molecular mass of 13 kDa. It was adsorbed on Affi-gel blue gel and CM-Sepharose. It exerted antifungal activity toward Mycosphaerella arachidicola and Physalospora piricola. In addition, the trypsin-chymotrypsin inhibitor elicited a mitogenic response from mouse splenocytes and inhibited the activity of human immunodeficiency virus-1 reverse transcriptase.

Identification of unique or elevated levels of kernel proteins in aflatoxin-resistant maize genotypes through proteome analysis

ABSTRACT Aflatoxins are carcinogens produced by Aspergillus flavus and A. parasiticus during infection of susceptible crops such as maize (Zea mays L.). Resistant maize genotypes have been identified, but the incorporation of resistance into commercial lines has been slow due to the lack of selectable markers. Here we report the identification of potential markers in resistant maize lines using a proteomics approach. Kernel embryo proteins from each of two resistant genotypes have been compared with those from a composite of five susceptible genotypes using large format two-dimensional gel electrophoresis. Through these comparisons, both quantitative and qualitative differences have been identified. Protein spots have been sequenced, and based on peptide sequence homology analysis, are categorized as follows: storage proteins (globulin 1 and globulin 2), late embryogenesis abundant (LEA) proteins related to drought or desiccation (LEA3 and LEA14), water- or osmo-stress related proteins (WSI18 and aldose reductase), and heat-stress related proteins (HSP16.9). Aldose reductase activity measured in resistant and susceptible genotypes before and after infection suggests the importance of constitutive levels of this enzyme to resistance. Results of this study point to a correlation between host resistance and stress tolerance. The putative function of each identified protein is discussed.

Transport of an antifungal trypsin inhibitor isolated from corn across the blood-brain barrier

We determined whether an antifungal 14-kDa protein trypsin inhibitor isolated from corn is able to cross the blood-brain barrier. We found that it completely crossed the blood-brain barrier by means of a saturable mechanism at a rate of 0.153 microl/g. min, with about 0.082% of the intravenously injected dose being taken up per gram of brain.

A Bowman-Birk-type trypsin-chymotrypsin inhibitor from broad beans

An isolation procedure comprising affinity chromatography on Affi-gel blue gel, ion exchange chromatography on SP-Toyopearl, and fast protein liquid chromatography on Mono S was used to purify a peptide from broad beans which manifested antifungal activity toward Mycosphaerella arachidicola, Fusarium oxysporum, and Botrytis cinerea. The peptide demonstrated a molecular mass of 7.5 kDa. N-terminal sequence analysis disclosed the identity of the antifungal peptide to be a trypsin-chymotrypsin inhibitor. The trypsin-chymotrypsin inhibitor also exerted an inhibitory action on chymotrypsin activity and HIV-1 reverse transcriptase activity. Proliferation of murine splenocytes was stimulated in the presence of the trypsin-chymotrypsin inhibitor. This report constitutes the first observation of antifungal activity of a leguminous peptidic protease inhibitor.

Comparison of constitutive and inducible maize kernel proteins of genotypes resistant or susceptible to aflatoxin production

Maize genotypes resistant or susceptible to aflatoxin production or contamination were compared for differences in both constitutive and inducible proteins. Five additional constitutive proteins were found to be associated with resistance in over 8 of the 10 genotypes examined. Among these, the 58- and 46-kDa proteins were identified as globulin-1 and globulin-2, respectively. Differences in the ability to induce specific antifungal proteins, such as the higher synthesis of the 22-kDa zeamatin in resistant genotypes, were also observed between resistant and susceptible kernels incubated under germinating conditions (31 degrees C, 100% humidity). Both constitutive and inducible proteins appear to be necessary for kernel resistance. Embryo-killed kernels (unable to synthesize new proteins) supported the highest level of aflatoxins, whereas imbibed kernels (to hasten protein induction) supported the lowest among all treatments. This suggests that the synthesis of new proteins by the embryo plays an important role in conferring resistance. However, significantly lower levels of aflatoxin production in embryo-killed resistant kernels than in susceptible ones suggest that, in reality, high levels of constitutive antifungal proteins are indispensable to kernel resistance.

Inhibition of growth of Aspergillus flavus and fungal alpha-amylases by a lectin-like protein from Lablab purpureus

Aspergillus flavus is a fungal pathogen of maize causing an important ear rot disease when plants are exposed to drought and heat stress. Associated with the disease is the production of aflatoxins, which are a series of structurally related mycotoxins known to be carcinogenic. Previous research has suggested that the alpha-amylase of A. flavus promotes aflatoxin production in the endosperm of infected maize kernels. We report here the isolation and characterization of a 36-kDa alpha-amylase inhibitor from Lablab purpureus (AILP). AILP inhibited the alpha-amylases from several fungi but had little effect on those from animal and plant sources. The protein inhibited conidial germination and hyphal growth of A. flavus. The amino acid sequence indicated that AILP is similar to lectin members of a lectin-arcelin-alpha-amylase inhibitor family described in common bean and shown to be a component of plant resistance to insect pests. AILP also agglutinated papain-treated red blood cells from human and rabbit. These data indicate that AILP represents a novel variant in the lectin-arcelin-alpha-amylase inhibitor family of proteins having lectin-like and alpha-amylase inhibitory activity.

Variation in in vitro alpha-amylase and protease activity is related to the virulence of Aspergillus flavus isolates

Variation in the ability of Aspergillus flavus isolates to spread between cotton boll locules was previously shown to be at least partially related to variation in the production of a specific polygalacturonase (pectinase P2C). To determine if non-pectolytic hydrolase differences between low- and high-virulence isolates exist and, thus, could also potentially contribute to virulence differences, the present investigation was undertaken. Two A. flavus isolates, AF12 with low virulence and lacking pectinase P2C and AF13 with high virulence and producing pectinase P2C, were compared for production of nonpectolytic hydrolases after growth in 10% potato dextrose broth. Activity of amylases, cellulases, xylanases, and proteases was quantified using the radial diffusion/cup plate technique followed by differential staining. Culture filtrates also were subjected to native polyacrylamide gel electrophoresis. Both isolates produced amylases, proteases, and xylanases, whereas cellulases were not detected for either. AF13 produced more amylase than AF12, and this difference was supported by amylase isoform differences between isolates on native polyacrylamide gel electrophoresis gels. AF13 also produced more protease than AF12; however, isoform differences between isolates were inconclusive. These variations in other hydrolytic activities (besides pectinases) may contribute to virulence differences in cotton bolls between AF12 and AF13.