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Carbohydrate‐binding module 74 is a novel starch‐binding domain associated with large and multidomain α‐amylase enzymes
Author(s) -
Valk Vincent,
Lammerts van Bueren Alicia,
Kaaij Rachel M.,
Dijkhuizen Lubbert
Publication year - 2016
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.13745
Subject(s) - starch , amylopectin , amylose , carbohydrate binding module , amylase , biochemistry , chemistry , enzyme , binding domain , glycoside hydrolase , biology , binding site
Microbacterium aurum B8.A is a bacterium that originates from a potato starch‐processing plant and employs a GH 13 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 CBM 74 that assists MaAmyA in efficient pore formation in starch granules. Protein sequence‐based BLAST searches revealed that CBM 74 occurs widespread, but in bacteria only, and is often associated with large and multi‐domain α‐amylases containing family CBM 25 or CBM 26 domains. CBM 74 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 CBM 74 representatives are found in α‐amylases originating from human gut‐associated Bifidobacteria, where they may assist in resistant starch degradation. The CBM 74 domain thus may have a strong impact on the efficiency of RS digestion in the mammalian gastrointestinal tract.