In vitro comparison of protease activities in preparations from free-living (Panagrellus redivivus) and plant-parasitic (Meloidogyne incognita) nematodes using FMRFa and FMRFa-like peptides as substrates

Extracts prepared from the microbivorous nematode Panagrellus redivivus and the plant-parasitic nematode Meloidogyne incognita were used to provide general protease activities for peptide substrate screening and species comparisons. Each extract was evaluated for its ability to degrade a broad range of nematode FMRFamide-like peptides (FLPs), key regulatory messengers governing nematode growth and development. Clear quantitative differences between the two extracts were observed using FMRFamide as a substrate. Extract potency assessed at EC50 (μg/μ l extract protein for 50% substrate digestion) was 1.8-fold greater for P. redivivus than for M. incognita, and potency assessed at EC90 was 2.5-fold greater. An overall potency difference was also present when screening the digestion of 17 nematode FLPs, but it was not universal. The mean percentage digestion of eight of the 17 FLPs was greater (P P. redivivus extract (76.3 ± 8.2) than with M. incognita extract (38.1 ± 8.7), but the means for the other nine FLPs were not different. Three FLPs (KPSFVRFa, AQTFVRFa, RNKFEFIRFa) were degraded extensively by the extracts of both species, and two FLPs (SAPYDPNFLRFa, SAEPFGTMRFa) were degraded 2.9-fold and 5.3-fold greater, respectively, with M. incognita extract than with P. redivivus extract. The ability of each extract to degrade FMRFa and KSAYMRFa was significantly reduced by using peptide analogues containing single d-amino acid substitutions, and the substitution effects were positional. Both FMRFa and KSAYMRFa were competitive substrates for aminopeptidases in each extract, but only the competitive ability of FMRFa was reduced by d-amino acid substitution. The variety and complexity of nematode FLP degradation by preparations representing phylogenetically and developmentally different nematode sources are discussed.