GtfC Enzyme of Geobacillus sp. 12AMOR1 Represents a Novel Thermostable Type of GH70 4,6-α-Glucanotransferase That Synthesizes a Linear Alternating (α1 → 6)/(α1 → 4) α-Glucan and Delays Bread Staling

Starch-acting alpha-glucanotransferase enzymes are of great interest for applications in the food industry. In previous work, we have characterized various 4,6- and 4,3-alpha-glucanotransferases of the glycosyl hydrolase (GH) family 70 (subfamily GtfB), synthesizing linear or branched alpha-glucans. Thus far, GtfB enzymes have only been identified in mesophilic Lactobacilli. Database searches showed that related GtfC enzymes occur in Gram-positive bacteria of the genera Exiguobacterium, Bacillus, and Geobacillus, adapted to growth at more extreme temperatures. Here, we report characteristics of the Geobacillus sp. 12AMOR1 GtfC enzyme, with an optimal reaction temperature of 60 degrees C and a melting temperature of 68 degrees C, allowing starch conversions at relatively high temperatures. This thermostable 4,6-alpha-glucanotransferase has a novel product specificity, cleaving off predominantly maltose units from amylose, attaching them with an (alpha 1 -> 6)-linkage to acceptor substrates. In fact, this GtfC represents a novel maltogenic aamylase. Detailed structural characterization of its starch-derived alpha-glucan products revealed that it yielded a unique polymer with alternating (alpha 1 -> 6)/(alpha 1 -> 4)-linked glucose units but without branches. Notably, this Geobacillus sp. 12AMOR1 GtfC enzyme showed clear antistaling effects in bread bakery products.

Automated summary

The study reports a novel thermostable starch-acting enzyme Geobacillus sp. 12AMOR1 GtfC, which has the ability to synthesize starch at high temperatures and shows anti-staling effects in bread bakery products.