title: AMP-activated protein kinase β-subunit requires internal motion for optimal carbohydrate binding.
abstract: AMP-activated protein kinase interacts with oligosaccharides and glycogen through the carbohydrate-binding module (CBM) containing the β-subunit, for which there are two isoforms (β(1) and β(2)). Muscle-specific β(2)-CBM, either as an isolated domain or in the intact enzyme, binds carbohydrates more tightly than the ubiquitous β(1)-CBM. Although residues that contact carbohydrate are strictly conserved, an additional threonine in a loop of β(2)-CBM is concurrent with an increase in flexibility in β(2)-CBM, which may account for the affinity differences between the two isoforms. In contrast to β(1)-CBM, unbound β(2)-CBM showed microsecond-to-millisecond motion at the base of a β-hairpin that contains residues that make critical contacts with carbohydrate. Upon binding to carbohydrate, similar microsecond-to-millisecond motion was observed in this β-hairpin and the loop that contains the threonine insertion. Deletion of the threonine from β(2)-CBM resulted in reduced carbohydrate affinity. Although motion was retained in the unbound state, a significant loss of motion was observed in the bound state of the β(2)-CBM mutant. Insertion of a threonine into the background of β(1)-CBM resulted in increased ligand affinity and flexibility in these loops when bound to carbohydrate. However, these mutations indicate that the additional threonine is not solely responsible for the differences in carbohydrate affinity and protein dynamics. Nevertheless, these results suggest that altered protein dynamics may contribute to differences in the ligand affinity of the two naturally occurring CBM isoforms.
authors.affiliation: Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Bieri
authors.forename: Jesse I
authors.initials: JI
authors.lastname: Mobbs
authors.forename: Ann
authors.initials: A
authors.lastname: Koay
authors.forename: Gavin
authors.initials: G
authors.lastname: Louey
authors.forename: Yee-Foong
authors.initials: YF
authors.lastname: Mok
authors.forename: Danny M
authors.initials: DM
authors.lastname: Hatters
authors.forename: Jong-Tae
authors.initials: JT
authors.lastname: Park
authors.forename: Kwan-Hwa
authors.initials: KH
authors.lastname: Park
authors.forename: Dietbert
authors.initials: D
authors.lastname: Neumann
authors.forename: David
authors.initials: D
authors.lastname: Stapleton
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gooley
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D050260:Carbohydrate Metabolism; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009068:Movement; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity
chemical_list: D055372:AMP-Activated Protein Kinases