PA1b binds to basic 7S globulin (BG) and stimulates its phosphorylation activity. Involved in the signal transduction system to regulate the growth and differentiation as a hormone peptide (By similarity). Toxic to various insects through binding to a high affinity binding site in the insect gut. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. The C-terminal glycine may be removed from PA1b.