FKRP

This gene encodes a protein which is targeted to the medial Golgi apparatus and is necessary for posttranslational modification of dystroglycan. Mutations in this gene have been associated with congenital muscular dystrophy, cognitive disability, and cerebellar cysts. Several alternatively spliced transcript variants of this gene have been described, but the full-length nature of some of these variants has not been determined. [provided by RefSeq, Oct 2008]

Full Name

Fukutin Related Protein

Function

Catalyzes the transfer of CDP-ribitol to ribitol 5-phosphate previously attached by FKTN/fukutin of to the phosphorylated O-mannosyl trisaccharide (N-acetylgalactosamine-beta-3-N-acetylglucosamine-beta-4-(phosphate-6-)mannose), a carbohydrate structure present in alpha-dystroglycan (DAG1) (PubMed:25279699, PubMed:26923585, PubMed:29477842).

This constitutes the second step in the formation of the ribose 5-phosphate tandem repeat which links the phosphorylated O-mannosyl trisaccharide to the ligand binding moiety composed of repeats of 3-xylosyl-alpha-1,3-glucuronic acid-beta-1 (PubMed:25279699, PubMed:26923585, PubMed:29477842).

Biological Process

Protein O-linked mannosylation Source: UniProtKB
Protein processing Source: Ensembl

Cellular Location

Golgi apparatus membrane; Secreted; Cytoplasm; Rough endoplasmic reticulum; Sarcolemma. According to some studies the N-terminal hydrophobic domain is cleaved after translocation to the Golgi apparatus and the protein is secreted (PubMed:19900540). Localization at the cell membrane may require the presence of dystroglycan (By similarity). At the Golgi apparatus localizes to the middle-to-trans-cisternae, as assessed by MG160 colocalization. Detected in rough endoplasmic reticulum in myocytes (PubMed:17554798, PubMed:21886772). In general, mutants associated with severe clinical phenotypes are retained within the endoplasmic reticulum (PubMed:15213246).

Involvement in disease

Muscular dystrophy-dystroglycanopathy congenital with brain and eye anomalies A5 (MDDGA5):
An autosomal recessive disorder characterized by congenital muscular dystrophy associated with cobblestone lissencephaly and other brain anomalies, eye malformations, profound mental retardation, and death usually in the first years of life. Included diseases are the more severe Walker-Warburg syndrome and the slightly less severe muscle-eye-brain disease.
Muscular dystrophy-dystroglycanopathy congenital with or without mental retardation B5 (MDDGB5):
A congenital muscular dystrophy characterized by a severe phenotype with inability to walk, muscle hypertrophy, marked elevation of serum creatine kinase, secondary deficiency of laminin alpha2, and a marked reduction in alpha-dystroglycan expression. Only a subset of affected individuals have brain involvements.
Muscular dystrophy-dystroglycanopathy limb-girdle C5 (MDDGC5):
An autosomal recessive degenerative myopathy with age of onset ranging from childhood to adult life, and variable severity. Clinical features include proximal muscle weakness, waddling gait, calf hypertrophy, cardiomyopathy and respiratory insufficiency. A reduction of alpha-dystroglycan and laminin alpha-2 expression can be observed on skeletal muscle biopsy from MDDGC5 patients.

Topology

Cytoplasmic: 1-6
Helical: 7-29
Lumenal: 30-495

PTM

N-glycosylated.