Evidence of the Involvement of Asparagine Deamidation in the Formation of Cyclodextrin Glycosyltransferase Isoforms in Paenibacillus sp. RB01

Cyclodextrin glycosyltransferase (CGTase) from Paenibacillus sp. RB01 and its recombinant enzyme exhibit three isoforms (I, II, and III) with the same apparent size but different charge. Here, we demonstrate for the first time that the deamidation of labile Asns causes the change in molecular forms of CGTase. The faster increase in number of isoforms was observed upon incubation in deamidation buffer at the more alkaline pH. The increase in levels of isoform II and III over time correlated with the increase in isoaspartate, a unique deamidation product. The predicted labile Asns were individually mutated to Asp, then the selected mutant and wild type isoforms were tryptic digested and labile Asns were investigated by MALDI-TOF. From the results, Asn427 was the most susceptible residue for deamidation, followed by Asn336, Asn415, and Asn567. In addition, Gln389 might also share a role. The advantage of using appropriate CGTase isoform in cyclodextrin production is reported.