Fukutin and fukutin-related protein (FKRP)

Abstract

Abnormal glycosylation of proteins is often associated with human diseases. A group of muscular dystrophy, dystroglycanopathy, is caused by abnormal glycosylation of dystroglycan (DG), a cell-surface laminin receptor. Fukutin (gene symbol, FKTN) and fukutin-related protein (FKRP; gene symbol, FKRP) are putative glycosyltransferases involved in the synthesis of a unique glycan structure of α-DG (Fig. 105.1), which is required for laminin-binding activity. Both genes were originally identified as causative genes of muscular dystrophies: FKTN for Fukuyama congenital muscular dystrophy (FCMD) and FKRP for congenital muscular dystrophy 1C (MDC1C) and limb-girdle type 2I (LGMD2I). Mutations in FKTN or FKRP lead to abnormal glycosylation and subsequent reduction of the ligand-binding activity of α-DG, which is associated with the pathology of the skeletal muscle, cardiac muscle, and the central nervous system. Consistently, studies using genetically modified animals support that fukutin/FKRP-dependent modification plays biologically important roles such as the maintenance of muscle cell membrane integrity, cortical histogenesis, and normal ocular development.