1. Biochemistry and Chemical Biology
Download icon

B4GAT1 is the priming enzyme for the LARGE-dependent functional glycosylation of α-dystroglycan

Research Article
  • Cited 50
  • Views 1,982
  • Annotations
Cite this article as: eLife 2014;3:e03943 doi: 10.7554/eLife.03943

Abstract

Recent studies demonstrated that mutations in B3GNT1, an enzyme proposed to be involved in poly-N-acetyllactosamine synthesis, were causal for congenital muscular dystrophy with hypoglycosylation of α-dystroglycan (secondary dystroglycanopathies). Since defects in the O-mannosylation protein glycosylation pathway are primarily responsible for dystroglycanopathies and with no established O-mannose initiated structures containing a β3 linked GlcNAc known, we biochemically interrogated this human enzyme. Here we report this enzyme is not a β-1,3-N-acetylglucosaminyltransferase with catalytic activity towards β-galactose but rather a β-1,4-glucuronyltransferase, designated B4GAT1, towards both α- and β-anomers of xylose. The dual-activity LARGE enzyme is capable of extending products of B4GAT1 and we provide experimental evidence that B4GAT1 is the priming enzyme for LARGE. Our results further define the functional O-mannosylated glycan structure and indicate that B4GAT1 is involved in the initiation of the LARGE-dependent repeating disaccharide that is necessary for extracellular matrix protein binding to O-mannosylated α-dystroglycan that is lacking in secondary dystroglycanopathies.

Article and author information

Author details

  1. Jeremy L Praissman

    University of Georgia, Athens, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. David H Live

    University of Georgia, Athens, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Shuo Wang

    University of Georgia, Athens, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Annapoorani Ramiah

    University of Georgia, Athens, United States
    Competing interests
    The authors declare that no competing interests exist.
  5. Zoeisha S Chinoy

    University of Georgia, Athens, United States
    Competing interests
    The authors declare that no competing interests exist.
  6. Geert-Jan Boons

    University of Georgia, Athens, United States
    Competing interests
    The authors declare that no competing interests exist.
  7. Kelley W Moremen

    University of Georgia, Athens, United States
    Competing interests
    The authors declare that no competing interests exist.
  8. Lance Wells

    University of Georgia, Athens, United States
    For correspondence
    lwells@ccrc.uga.edu
    Competing interests
    The authors declare that no competing interests exist.

Reviewing Editor

  1. Suzanne R Pfeffer, Stanford University, United States

Publication history

  1. Received: July 9, 2014
  2. Accepted: October 1, 2014
  3. Accepted Manuscript published: October 3, 2014 (version 1)
  4. Version of Record published: November 11, 2014 (version 2)

Copyright

© 2014, Praissman et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 1,982
    Page views
  • 243
    Downloads
  • 50
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, Scopus, PubMed Central.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Download citations (links to download the citations from this article in formats compatible with various reference manager tools)

Open citations (links to open the citations from this article in various online reference manager services)

Further reading

    1. Biochemistry and Chemical Biology
    Maria Carmela Filomena et al.
    Research Article

    Myopalladin (MYPN) is a striated muscle-specific immunoglobulin domain-containing protein located in the sarcomeric Z-line and I-band. MYPN gene mutations are causative for dilated (DCM), hypertrophic and restrictive cardiomyopathy. In a yeast two-hybrid screening, MYPN was found to bind to titin in the Z-line, which was confirmed by microscale thermophoresis. Cardiac analyses of MYPN knockout (MKO) mice showed the development of mild cardiac dilation and systolic dysfunction, associated with decreased myofibrillar isometric tension generation and increased resting tension at longer sarcomere lengths. MKO mice exhibited a normal hypertrophic response to transaortic constriction (TAC), but rapidly developed severe cardiac dilation and systolic dysfunction, associated with fibrosis, increased fetal gene expression, higher intercalated disc fold amplitude, decreased calsequestrin-2 protein levels, and increased desmoplakin and SORBS2 protein levels. Cardiomyocyte analyses showed delayed Ca2+ release and reuptake in unstressed MKO mice as well as reduced Ca2+ spark amplitude post-TAC, suggesting that altered Ca2+ handling may contribute to the development of DCM in MKO mice.

    1. Biochemistry and Chemical Biology
    Xavier Portillo et al.
    Research Article Updated

    An RNA polymerase ribozyme that has been the subject of extensive directed evolution efforts has attained the ability to synthesize complex functional RNAs, including a full-length copy of its own evolutionary ancestor. During the course of evolution, the catalytic core of the ribozyme has undergone a major structural rearrangement, resulting in a novel tertiary structural element that lies in close proximity to the active site. Through a combination of site-directed mutagenesis, structural probing, and deep sequencing analysis, the trajectory of evolution was seen to involve the progressive stabilization of the new structure, which provides the basis for improved catalytic activity of the ribozyme. Multiple paths to the new structure were explored by the evolving population, converging upon a common solution. Tertiary structural remodeling of RNA is known to occur in nature, as evidenced by the phylogenetic analysis of extant organisms, but this type of structural innovation had not previously been observed in an experimental setting. Despite prior speculation that the catalytic core of the ribozyme had become trapped in a narrow local fitness optimum, the evolving population has broken through to a new fitness locale, raising the possibility that further improvement of polymerase activity may be achievable.