Regulatory subunit of multiple voltage-gated sodium channel complexes that play important roles in excitable membranes in brain, heart and skeletal muscle. Enhances the presence of the pore-forming alpha subunit at the cell surface and modulates channel gating characteristics and the rate of channel inactivation. Modulates the activity of a variety of pore-forming alpha subunits, such as SCN1A, SCN2A, SCN3A, SCN4A, SCN5A and SCN10A. Component of a voltage-sensitive sodium channel complex that consists of a pore-forming alpha subunit and one or more regulatory beta subunits. Interacts with SCN4A. Interacts with NFASC. Interacts with SCN10A (By similarity). Interacts with SCN1A. Interacts with SCN3A. Interacts with SCN5A. Interacts with SCN8A (By similarity). Detected at nodes of Ranvier on the sciatic nerve. Detected in hippocampus CA3 bipolar neurons (at protein level) (PubMed:19710327). Detected in skeletal muscle (PubMed:9013777). Belongs to the sodium channel auxiliary subunit SCN1B (TC 8.A.17) family.