Enzymatic potato starch modification and structure-function analysis of six diverse GH77 4-alpha-glucanotransferases

4-alpha-glucanotransferase (EC 2.4.1.25) mediated glucan transfer in starch provides opportunities for production of clean label starch ingredients with unique gelling properties. 4-alpha-glucanotransferases can be found in glycoside hydrolase (GH) family GH13, GH57, and in the monospecific glycoside hydrolase family 77 (GH77). Here, pH -temperature optima, steady-state kinetics, potato starch modifying properties and structural folds are reported for six phylogenetically distinct GH77 members, representing four different domain architectures including a novel multi-domain 4-alpha-glucanotransferase from Lactococcus lactis. Four of the enzymes exhibited starch modi-fying activity leading to a gradual decrease of the amylose content, elongation of amylopectin chains, and enabled formation of firm starch gels. Unexpectedly, these diverse enzymes catalyzed similar changes in chain length distributions. However, the amylose depletion and amylopectin elongation rates spanned more than two orders of magnitude between the enzyme showing very different specific activities. Tt4 alpha GT from Thermus ther-mophilus had highest temperature optimum (73 degrees C) and superior potato starch modifying efficacy compared to the other five enzymes.

Automated summary

4-alpha-glucanotransferase mediated glucan transfer allows for the production of clean label starch ingredients with unique gelling properties. Researchers have studied six different GH77 members and found that four of them exhibit starch modifying activity, leading to a decrease in amylose content, elongation of amylopectin chains, and the formation of firm starch gels. The enzyme Tt4 alpha GT from Thermus thermophilus showed the highest temperature optimum (73 degrees C) and the best potato starch modifying efficacy compared to the other enzymes.