Structural basis of glycogen branching enzyme deficiency and pharmacologic rescue by rational peptide design

Glycogen branching enzyme 1 (GBE1) plays an essential role in glycogen biosynthesis by generating α-1,6-glucosidic branches from α-1,4-linked glucose chains, to increase solubility of the glycogen polymer. Mutations in the GBE1 gene lead to the heterogeneous early-onset glycogen storage disorder typ...

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Bibliographic Details
Published in:Human molecular genetics 2015-10, Vol.24 (20), p.5667-5676
Main Authors: Froese, D Sean, Michaeli, Amit, McCorvie, Thomas J, Krojer, Tobias, Sasi, Meitav, Melaev, Esther, Goldblum, Amiram, Zatsepin, Maria, Lossos, Alexander, Álvarez, Rafael, Escribá, Pablo V, Minassian, Berge A, von Delft, Frank, Kakhlon, Or, Yue, Wyatt W
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Computational Biology
Glycogen Debranching Enzyme System - chemistry
Glycogen Debranching Enzyme System - drug effects
Glycogen Debranching Enzyme System - genetics
Glycogen Debranching Enzyme System - metabolism
Glycogen Storage Disease - drug therapy
Glycogen Storage Disease - enzymology
Glycogen Storage Disease - genetics
Glycogen Storage Disease Type IV - enzymology
Glycogen Storage Disease Type IV - genetics
Humans
Molecular Sequence Data
Mutation, Missense
Nervous System Diseases - drug therapy
Nervous System Diseases - enzymology
Nervous System Diseases - genetics
Peptides - therapeutic use
Protein Structure, Tertiary
Sequence Alignment
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Summary:Glycogen branching enzyme 1 (GBE1) plays an essential role in glycogen biosynthesis by generating α-1,6-glucosidic branches from α-1,4-linked glucose chains, to increase solubility of the glycogen polymer. Mutations in the GBE1 gene lead to the heterogeneous early-onset glycogen storage disorder type IV (GSDIV) or the late-onset adult polyglucosan body disease (APBD). To better understand this essential enzyme, we crystallized human GBE1 in the apo form, and in complex with a tetra- or hepta-saccharide. The GBE1 structure reveals a conserved amylase core that houses the active centre for the branching reaction and harbours almost all GSDIV and APBD mutations. A non-catalytic binding cleft, proximal to the site of the common APBD mutation p.Y329S, was found to bind the tetra- and hepta-saccharides and may represent a higher-affinity site employed to anchor the complex glycogen substrate for the branching reaction. Expression of recombinant GBE1-p.Y329S resulted in drastically reduced protein yield and solubility compared with wild type, suggesting this disease allele causes protein misfolding and may be amenable to small molecule stabilization. To explore this, we generated a structural model of GBE1-p.Y329S and designed peptides ab initio to stabilize the mutation. As proof-of-principle, we evaluated treatment of one tetra-peptide, Leu-Thr-Lys-Glu, in APBD patient cells. We demonstrate intracellular transport of this peptide, its binding and stabilization of GBE1-p.Y329S, and 2-fold increased mutant enzymatic activity compared with untreated patient cells. Together, our data provide the rationale and starting point for the screening of small molecule chaperones, which could become novel therapies for this disease.
ISSN:0964-6906
1460-2083
DOI:10.1093/hmg/ddv280