A broad range of enzymes are used to modify starch for various applications. Here, a thermophilic 4-α-glucanotransferase from
Thermoproteus uzoniensis (TuαGT) is engineered by N-terminal fusion of the starch binding domains (SBDs) of carbohydrate binding module family 20 (CBM20) to enhance its affinity
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A broad range of enzymes are used to modify starch for various applications. Here, a thermophilic 4-α-glucanotransferase from
Thermoproteus uzoniensis (TuαGT) is engineered by N-terminal fusion of the starch binding domains (SBDs) of carbohydrate binding module family 20 (CBM20) to enhance its affinity for granular starch. The SBDs are N-terminal tandem domains (SBD
St1 and SBD
St2) from
Solanum tuberosum disproportionating enzyme 2 (
StDPE2) and the C-terminal domain (SBD
GA) of glucoamylase from
Aspergillus niger (
AnGA). In silico analysis of CBM20s revealed that SBD
GA and copies one and two of GH77 DPE2s belong to well separated clusters in the evolutionary tree; the second copies being more closely related to non-CAZyme CBM20s. The activity of SBD-TuαGT fusions increased 1.2–2.4-fold on amylose and decreased 3–9 fold on maltotriose compared with TuαGT. The fusions showed similar disproportionation activity on gelatinised normal maize starch (NMS). Notably, hydrolytic activity was 1.3–1.7-fold elevated for the fusions leading to a reduced molecule weight and higher α-1,6/α-1,4-linkage ratio of the modified starch. Notably, SBD
GA-TuαGT and-SBD
St2-TuαGT showed
Kd of 0.7 and 1.5 mg/mL for waxy maize starch (WMS) granules, whereas TuαGT and SBD
St1-TuαGT had 3–5-fold lower affinity. SBD
St2 contributed more than SBD
St1 to activity, substrate binding, and the stability of TuαGT fusions.
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