title: Degradation of Granular Starch by the Bacterium Microbacterium aurum Strain B8.A Involves a Modular α-Amylase Enzyme System with FNIII and CBM25 Domains.
abstract: The bacterium Microbacterium aurum strain B8.A, originally isolated from a potato plant wastewater facility, is able to degrade different types of starch granules. Here we report the characterization of an unusually large, multidomain M. aurum B8.A α-amylase enzyme (MaAmyA). MaAmyA is a 1,417-amino-acid (aa) protein with a predicted molecular mass of 148 kDa. Sequence analysis of MaAmyA showed that its catalytic core is a family GH13_32 α-amylase with the typical ABC domain structure, followed by a fibronectin (FNIII) domain, two carbohydrate binding modules (CBM25), and another three FNIII domains. Recombinant expression and purification yielded an enzyme with the ability to degrade wheat and potato starch granules by introducing pores. Characterization of various truncated mutants of MaAmyA revealed a direct relationship between the presence of CBM25 domains and the ability of MaAmyA to form pores in starch granules, while the FNIII domains most likely function as stable linkers. At the C terminus, MaAmyA carries a 300-aa domain which is uniquely associated with large multidomain amylases; its function remains to be elucidated. We concluded that M. aurum B8.A employs a multidomain enzyme system to initiate degradation of starch granules via pore formation.
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands v.valk@rug.nl l.dijkhuizen@rug.nl.
authors.forename: Vincent
authors.initials: V
authors.lastname: Valk
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands.
authors.forename: Wieger
authors.initials: W
authors.lastname: Eeuwema
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands.
authors.forename: Fean D
authors.initials: FD
authors.lastname: Sarian
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands.
authors.forename: Rachel M
authors.initials: RM
authors.lastname: van der Kaaij
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands v.valk@rug.nl l.dijkhuizen@rug.nl.
authors.forename: Lubbert
authors.initials: L
authors.lastname: Dijkhuizen
mesh_terms: D000192:Actinomycetales / Q000737:chemistry / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D011198:Solanum tuberosum / Q000378:metabolism; D013213:Starch / Q000378:metabolism*; D000516:alpha-Amylases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D013213:Starch; D000516:alpha-Amylases