Modulates channel gating kinetics. Causes negative shifts in the voltage dependence of activation of certain alpha sodium channels, but does not affect the voltage dependence of inactivation. Modulates the susceptibility of the sodium channel to inhibition by toxic peptides from spider, scorpion, wasp and sea anemone venom (By similarity). The voltage-sensitive sodium channel consists of an ion conducting pore forming alpha-subunit (SCN2A) regulated by one or more beta subunits (SCN1B, SCN2B, SCN3B and SCN4B). SCN1B and SCN3B are non-covalently associated with SCN2A. SCN2B and SCN4B are disulfide-linked to SCN2A (By similarity). Contains an interchain disulfide bond with SCN2A. N-glycosylated. Belongs to the sodium channel auxiliary subunit SCN4B (TC 8.A.17) family.