Characterisation of the effects on proteases of Heterodera glycines and Meloidogyne incognita second-stage juveniles by inhibitors obtained from cysts of H. glycines

The protease inhibitor component of Heterodera glycines cyst contents was explored using a battery of peptide substrates and H. glycines and Meloidogyne incognita second-stage juveniles as enzyme sources. Protease inhibitors were prepared by heat-denaturing H. glycines cyst-egg extract (hHglCE), which was used in all inhibition exploration. Eight substrates targeting four endoprotease groups (aspartic, cysteine, metallo- and serine proteases) revealed that protease inhibition by hHglCE varied significantly between H. glycines and M. incognita with seven of the eight substrates. Only cysteine protease activity was inhibited equally between H. glycines and M. incognita. Aspartic protease activity was inhibited more strongly in H. glycines and serine protease activity was inhibited more strongly in M. incognita. Digestion of five matrix metalloprotease (MMP) substrates was inhibited more strongly in H. glycines (two substrates) and M. incognita (three substrates). These variations were particularly intriguing given the potential association of MMP proteases with developing embryos. Inhibition of digestion of nematode FMRFamide-like peptides (FLPs) showed less variation between nematode species than the targeted substrates, but inhibition did vary significantly across substrates within each species. Digestion of FLP-6 was the least affected by hHglCE but was inhibited significantly more in M. incognita than in H. glycines. Residue differences between two FLP-14 sequences significantly affected inhibition of FLP-14 digestion in both H. glycines and M. incognita. RP-HPLC fractionation of hHglCE clearly demonstrated the presence of high (Fr No.5) and low (Fr No.14) polarity inhibitor components. Potency of inhibition of M. incognita serine protease activity, based upon IC50 values (1.68 and 2.78 hHglCEeq reaction−1 for Fr No.5 and Fr No.14, respectively), was reduced significantly from unfractionated hHglCE (IC50 = 0.61), suggesting inhibitor dilution, loss of component synergy, or both, due to fractionation.

Evaluation of proteases and protease inhibitors in Heterodera glycines cysts obtained from laboratory and field populations

Proteases and protease inhibitors were evaluated in preparations ofHeterodera glycinescysts (nHglCE) obtained from glasshouse cultures (GH) and a field (LR) population. Using a FRET-peptide library comprising 512 peptide substrate pools that detect four endoprotease types (aspartic, cysteine, metallo- and serine), we found that the relative distributions of six endoproteases within the four catalytic types were similar among GH and LR preparations. However, levels of mean protease activity ( s−1(μg nHglCE)−1) across all 512 pools varied nearly eight-fold among the preparations. This variation was not related to cyst source. These qualitative (type distribution) and quantitative relationships persisted when analysis was restricted to the top 40% (activity) pools. Analysis of the top 4% of activity pools revealed some substrate cleavage site preferences between the GH and LR proteases. GH and LR preparations also differed significantly in digestion rates of trypsin and matrix metalloprotease (MMP) substrates, with LR rates two-fold greater than GH rates for each protease. By contrast, inhibition of trypsin activity inMeloidogyne incognitaextracts by heat-denatured preparations (hHglCE) was 1.6-fold greater with GH hHglCE than with LR hHglCE. Inhibition of MMP activity was the same (>60%) for each hHglCE. Fractionation of GH and LR hHglCE preparations by RP-HPLC (CH3CN/0.1% TFA system) yielded protease inhibition profiles that were similar for GH and LR. MMP inhibitors eluted at 35-40% CH3CN, and trypsin inhibitors eluted at both 5% and 35-40% CH3CN, suggesting the possibility of peptide as well as other small molecular weight inhibitors. These discoveries illustrate the importance of examiningH. glycinescysts as a source of materials for novel nematode controls.