Carbohydrate-binding module 74 is a novel starch-binding domain associated with large and multidomain α-amylase enzymes.
Microbacterium aurum B8.A is a bacterium that originates from a potato starch-processing plant and employs a GH13 α-amylase (MaAmyA) enzyme that forms pores in potato starch granules. MaAmyA is a large and multi-modular protein that contains a novel domain at its C terminus (Domain 2). Deletion of Domain 2 from MaAmyA did not affect its ability to degrade starch granules but resulted in a strong reduction in granular pore size. Here, we separately expressed and purified this Domain 2 in Escherichia coli and determined its likely function in starch pore formation. Domain 2 independently binds amylose, amylopectin, and granular starch but does not have any detectable catalytic (hydrolytic or oxidizing) activity on α-glucan substrates. Therefore, we propose that this novel starch-binding domain is a new carbohydrate-binding module (CBM), the first representative of family CBM74 that assists MaAmyA in efficient pore formation in starch granules. Protein sequence-based BLAST searches revealed that CBM74 occurs widespread, but in bacteria only, and is often associated with large and multi-domain α-amylases containing family CBM25 or CBM26 domains. CBM74 may specifically function in binding to granular starches to enhance the capability of α-amylase enzymes to degrade resistant starches (RSs). Interestingly, the majority of family CBM74 representatives are found in α-amylases originating from human gut-associated Bifidobacteria, where they may assist in resistant starch degradation. The CBM74 domain thus may have a strong impact on the efficiency of RS digestion in the mammalian gastrointestinal tract.
Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), The Netherlands.
Vincent
V
Valk
Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), The Netherlands.
Alicia
A
Lammerts van Bueren
Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), The Netherlands.
Rachel M
RM
van der Kaaij
Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), The Netherlands.
Lubbert
L
Dijkhuizen
D039903:Actinobacteria / Q000201:enzymology; D001644:Bifidobacterium / Q000201:enzymology; D050260:Carbohydrate Metabolism; D004063:Digestion / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D000069196:Gastrointestinal Microbiome / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D005936:Glucans / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D000072417:Protein Domains / Q000235:genetics; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011198:Solanum tuberosum / Q000737:chemistry; D013213:Starch / Q000737:chemistry / Q000378:metabolism*; D000516:alpha-Amylases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D005936:Glucans; D011956:Receptors, Cell Surface; C055213:saccharide-binding proteins; D013213:Starch; D000516:alpha-Amylases
CBM74; granular starch; resistant starch; starch-binding domain; α-amylase