Fukutin-related Protein Resides in the Golgi Cisternae of Skeletal Muscle Fibres and Forms Disulfide-Linked Homodimers via an N-terminal Interaction

PLoS One. 2011;6(8):e22968. doi: 10.1371/journal.pone.0022968. Epub 2011 Aug 23.

Abstract

Limb-Girdle Muscular Dystrophy type 2I (LGMD2I) is an inheritable autosomal, recessive disorder caused by mutations in the FuKutin-Related Protein (FKRP) gene (FKRP) located on chromosome 19 (19q13.3). Mutations in FKRP are also associated with Congenital Muscular Dystrophy (MDC1C), Walker-Warburg Syndrome (WWS) and Muscle Eye Brain disease (MEB). These four disorders share in common an incomplete/aberrant O-glycosylation of the membrane/extracellular matrix (ECM) protein α-dystroglycan. However, further knowledge on the FKRP structure and biological function is lacking, and its intracellular location is controversial. Based on immunogold electron microscopy of human skeletal muscle sections we demonstrate that FKRP co-localises with the middle-to-trans-Golgi marker MG160, between the myofibrils in human rectus femoris muscle fibres. Chemical cross-linking experiments followed by pairwise yeast 2-hybrid experiments, and co-immune precipitation, demonstrate that FKRP can exist as homodimers as well as in large multimeric protein complexes when expressed in cell culture. The FKRP homodimer is kept together by a disulfide bridge provided by the most N-terminal cysteine, Cys6. FKRP contains N-glycan of high mannose and/or hybrid type; however, FKRP N-glycosylation is not required for FKRP homodimer or multimer formation. We propose a model for FKRP which is consistent with that of a Golgi resident type II transmembrane protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biomarkers / metabolism
  • Cell Line
  • Cell Survival / drug effects
  • Cysteine / metabolism
  • Disulfides / metabolism*
  • Dithiothreitol / pharmacology
  • Glycosylation / drug effects
  • Golgi Apparatus / drug effects
  • Golgi Apparatus / metabolism*
  • Golgi Apparatus / ultrastructure
  • Humans
  • Immunoprecipitation
  • Mannose / metabolism
  • Models, Biological
  • Multiprotein Complexes / metabolism
  • Muscle Fibers, Skeletal / drug effects
  • Muscle Fibers, Skeletal / metabolism*
  • Muscle Fibers, Skeletal / ultrastructure
  • Myofibrils / drug effects
  • Myofibrils / metabolism
  • Myofibrils / ultrastructure
  • Oligosaccharides / metabolism
  • Oxidation-Reduction / drug effects
  • Pentosyltransferases
  • Protein Binding / drug effects
  • Protein Multimerization* / drug effects
  • Protein Transport / drug effects
  • Proteins / metabolism*
  • Receptors, Fibroblast Growth Factor / metabolism
  • Recombinant Proteins / metabolism
  • Sialoglycoproteins / metabolism
  • Two-Hybrid System Techniques

Substances

  • Biomarkers
  • Disulfides
  • Multiprotein Complexes
  • Oligosaccharides
  • Proteins
  • Receptors, Fibroblast Growth Factor
  • Recombinant Proteins
  • Sialoglycoproteins
  • cysteine-rich fibroblast growth factor receptor
  • FKRP protein, human
  • Pentosyltransferases
  • Cysteine
  • Mannose
  • Dithiothreitol