Stimulates the activity of serine palmitoyltransferase (SPT). The composition of the serine palmitoyltransferase (SPT) complex determines the substrate preference, complexes with this subunit showing a clear preference for longer acyl-CoAs. The SPTLC1-SPTLC2-SPTSSB complex shows a strong preference for C18-CoA substrate, while the SPTLC1-SPTLC3-SPTSSB isozyme displays an ability to use a broader range of acyl-CoAs, without apparent preference. May play a role in signal transduction. Lipid metabolism; sphingolipid metabolism. Interacts with SPTLC1; the interaction is direct. Component of the serine palmitoyltransferase (SPT) complex, composed of SPTLC1, either SPTLC2 or SPTLC3, and either SPTSSA or SPTSSB. Expression is seen predominantly in the prostate epithelium with weaker expression in the fibroblasts and endothelial cells. Expression is suppressed by androgens in the androgen-sensitive LNCaP cell line. Belongs to the SPTSS family. SPTSSB subfamily.