Glycogen synthase kinase-3 (GSK-3) sequentially phosphorylates four serine residues on glycogen synthase (GS), in the sequence SxxxSxxxSxxx-SxxxS(p), by recognising and phosphorylating the first serine in the sequence motif SxxxS(P) (where S(p) represents a phosphoserine). Interaction of GSK-3 with a peptide derived from GSK-3 binding protein (this family) prevents GSK-3 interaction with Axin. This interaction thereby inhibits the Axin-dependent phosphorylation of beta-catenin by GSK-3 [1].

1: The structure of phosphorylated GSK-3beta complexed with a peptide, FRATtide, that inhibits beta-catenin phosphorylation. Bax B, Carter PS, Lewis C, Guy AR, Bridges A, Tanner R, Pettman G, Mannix C, Culbert AA, Brown MJ, Smith DG, Reith AD; Structure (Camb) 2001;9:1143-1152. PMID:11738041