Characterization of the branching patterns of glycogen branching enzyme truncated on the N-terminus

Truncation of 112 amino acids at the N-terminus (Nd 1–112) changes the chain transfer pattern of the Escherichia coli glycogen branching enzyme (GBE) [Arch. Biochem. Biophys. 397 (2002) 279]. We investigated further the role of the N-terminus by engineering other truncated GBEs and analyzing the branching pattern by high-performance anion-exchange chromatography. The wild type GBE transfers mainly chains with a degree of polymerization (d.p.) of 8–14, the Nd 1–112 enzyme transfers a greater proportion of chains with higher d.p. 15–20, whereas the 63- and 83-amino acid deleted enzymes had an intermediate pattern of transferred chains (d.p. 10–20). These data showed that a progressive shortening of the N-terminus leads to a gradual increase in the length of the transferred chains, suggesting that the N-terminus provides a support for the glucan substrate during the processes of cleavage and transfer of the α-(1–4) glucan chains.