Title :
Fukutin-related protein resides in the Golgi cisternae of skeletal muscle fibres and forms disulfide-linked
homodimers via an N-terminal interaction
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