title: The characterization of modified starch branching enzymes: toward the control of starch chain-length distributions.
abstract: Starch is a complex branched glucose polymer whose branch molecular weight distribution (the chain-length distribution, CLD) influences nutritionally important properties such as digestion rate. Chain-stopping in starch biosynthesis is by starch branching enzyme (SBE). Site-directed mutagenesis was used to modify SBEIIa from Zea mays (mSBEIIa) to produce mutants, each differing in a single conserved amino-acid residue. Products at different times from in vitro branching were debranched and the time evolution of the CLD measured by size-exclusion chromatography. The results confirm that Tyr352, Glu513, and Ser349 are important for mSBEIIa activity while Arg456 is important for determining the position at which the linear glucan is cut. The mutant mSBEIIa enzymes have different activities and suggest the length of the transferred chain can be varied by mutation. The work shows analysis of the molecular weight distribution can yield information regarding the enzyme branching sites useful for development of plants yielding starch with improved functionality.
authors: Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei, China; Centre for Nutrition and Food Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia.
authors: Cheng
authors: C
authors: Li
authors: Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei, China; Centre for Nutrition and Food Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia.
authors: Alex Chi
authors: AC
authors: Wu
authors: Centre for Nutrition and Food Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia.
authors: Rob Marc
authors: RM
authors: Go
authors: Centre for Nutrition and Food Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia.
authors: Jacob
authors: J
authors: Malouf
authors: Centre for Nutrition and Food Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia; School of Agriculture and Food Sciences, The University of Queensland, Brisbane, QLD, Australia.
authors: Mark S
authors: MS
authors: Turner
authors: School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, Australia.
authors: Alpeshkumar K
authors: AK
authors: Malde
authors: School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, Australia.
authors: Alan E
authors: AE
authors: Mark
authors: Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei, China; Centre for Nutrition and Food Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia.
authors: Robert G
authors: RG
authors: Gilbert
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D002240:Carbohydrate Sequence; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D057075:Enzyme Assays; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015202:Protein Engineering; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013213:Starch / Q000096:biosynthesis* / Q000737:chemistry; D013329:Structure-Activity Relationship; D003313:Zea mays / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
chemical_list: D010940:Plant Proteins; D011994:Recombinant Proteins; D013213:Starch; D015061:1,4-alpha-Glucan Branching Enzyme