Serine endoprotease which cleaves preproteins at paired basic amino acids (PubMed:12657671, PubMed:15180830, PubMed:16945111, PubMed:23665919, PubMed:24671950). Processes FMRFamide-like (flp) and neuropeptide-like protein (nlp) neuropeptides (PubMed:12657671, PubMed:16945111). Probably by processing flp-1 and flp-18, modulates the neuronal excitation-inhibition balance and thus the level of activity of the locomotor circuit (PubMed:23658528). Regulates sensitivity to mechanosensory stimuli (PubMed:11717360). By processing neuropeptides, modulates basal acetylcholine release at the ventral cord neuromuscular junctions (PubMed:12657671). Probably by processing flp neuropeptides, regulates the turning step of male mating behavior (PubMed:17611271). Cleaves pro-insulin-like proteins ins-3, ins-4 and ins-6 into their mature active forms (PubMed:23665919, PubMed:24671950). Together with convertase kpc-1, cleaves pro-insulin-like protein ins-18 (PubMed:24671950). By controlling ins-4 and ins-6 processing and thus the activation of the daf-2/InsR pathway, negatively modulates synapse development and synaptic transmission at neuromuscular junctions (PubMed:23665919). Similarly, by controlling ins-4 and ins-6 processing, negatively regulates dauer formation under optimal environmental conditions (PubMed:24671950). Under adverse environmental conditions, may promote dauer formation by processing ins-18, a daf-2/InsR antagonist (PubMed:24671950). May cleave dense-core vesicle membrane protein ida-1 (PubMed:15180830). Involved in egg-laying, fat storage and locomotion (PubMed:11813735, PubMed:11717360, PubMed:17564681). Release of protein hormones and neuropeptides from their precursors, generally by hydrolysis of -Lys-Arg-|- bonds. Interacts (via C-terminus) with F-box protein fsn-1 (via SPRY domain); the interaction results in egl-3 proteasomal degradation. Expressed in head and tail ganglia (PubMed:7954663, PubMed:11717360, PubMed:12657671, PubMed:24671950). Expressed in neurons including mechanosensory and motor neurons, and interneurons (at protein level) (PubMed:11717360, PubMed:12657671). Expressed in the nerve ring, ventral nerve cord and intestine (PubMed:24671950). Ubiquitinated. Belongs to the peptidase S8 family. Furin subfamily.