Pijning Tjaard, Gangoiti Joana, Te Poele Evelien M, Börner Tim, Dijkhuizen Lubbert
Biomolecular X-ray Crystallography, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, Groningen 9747 AG, The Netherlands.
Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, Groningen 9747 AG, The Netherlands.
J Agric Food Chem. 2021 Nov 10;69(44):13235-13245. doi: 10.1021/acs.jafc.1c05657. Epub 2021 Oct 28.
GtfB-type α-glucanotransferase enzymes from glycoside hydrolase family 70 (GH70) convert starch substrates into α-glucans that are of interest as food ingredients with a low glycemic index. Characterization of several GtfBs showed that they differ in product- and substrate specificity, especially with regard to branching, but structural information is limited to a single GtfB, preferring mostly linear starches and featuring a tunneled binding groove. Here, we present the second crystal structure of a 4,6-α-glucanotransferase ( NCC 2613) and an improved homology model of a 4,3-α-glucanotransferase GtfB ( NCC 2970) and show that they are able to convert both linear and branched starch substrates. Compared to the previously described GtfB structure, these two enzymes feature a much more open binding groove, reminiscent of and evolutionary closer to starch-converting GH13 α-amylases. Sequence analysis of 287 putative GtfBs suggests that only 20% of them are similarly "open" and thus suitable as broad-specificity starch-converting enzymes.
糖苷水解酶家族70（GH70）中的GtfB型α-葡聚糖转移酶可将淀粉底物转化为α-葡聚糖，作为具有低血糖指数的食品成分备受关注。对几种GtfB的表征表明，它们在产物和底物特异性方面存在差异，尤其是在分支方面，但结构信息仅限于单个GtfB，其大多偏好线性淀粉且具有隧道状结合凹槽。在此，我们展示了4,6-α-葡聚糖转移酶（NCC 2613）的第二个晶体结构以及4,3-α-葡聚糖转移酶GtfB（NCC 2970）的改进同源模型，并表明它们能够转化线性和分支淀粉底物。与先前描述的GtfB结构相比，这两种酶具有更开放的结合凹槽，让人联想到淀粉转化型GH13α-淀粉酶且在进化上更接近。对287种假定的GtfB进行序列分析表明，其中只有20%同样“开放”，因此适合作为具有广泛特异性的淀粉转化酶。
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