Component of a SCF (SKP1-CUL1-F-box protein) E3 ubiquitin ligase complex which is required for the restriction and/or maturation of synapses in GABAergic neuromuscular junction (NMJ) presynaptic neurons. Promotes NRJ synapse development and synaptic transmission by negatively regulating the daf-2/InsR pathway in muscles. By targeting convertase egl-3 for degradation, negatively modulates insulin-like protein ins-4 and ins-6 processing. May stabilize synapse formation by promoting the down-regulation of scd-2. Regulates axon termination in PLM and ALM neurons. Protein modification; protein ubiquitination. Component of an SCF (SKP1-CUL1-F-box protein) E3 ubiquitin ligase complex composed of cul-1, fsn-1, rpm-1 and skr-1. Interacts (via SPRY domain) with scd-2 (via cytoplasmic domain). Interacts (via SPRY domain) with convertase egl-3 (via C-terminus). Belongs to the FBXO45/Fsn family.