Title : Missense mutations in
ABCG5 and
ABCG8 disrupt heterodimerization and trafficking
Abstract :
- Mutations in ABCG5 ( G5 ) or ABCG8 ( G8 ) cause sitosterolemia, an autosomal recessive disease characterized by sterol accumulation and premature atherosclerosis
- G5 and G8 are ATP-binding cassette (ABC) half-transporters that must heterodimerize to move to the apical surface of cells
- We examined the role of N-linked glycans in the formation of the G5/G8 heterodimer to gain insight into the determinants of folding and trafficking of these proteins
- Site-directed mutagenesis revealed that two asparagine residues ( Asn(585) and Asn(592) ) are glycosylated in G5 and that G8 has a single N-linked glycan attached to Asn(619)
- N-Linked glycosylation of G8 was required for efficient trafficking of the G5/G8 heterodimer , but mutations that abolished glycosylation of G5 did not prevent trafficking of the heterodimer
- Both G5 and G8 are bound by the lectin chaperone, calnexin , suggesting that the calnexin cycle may facilitate folding of the G5/G8 heterodimer
- To determine the effects of 13 disease-causing missense mutations in G5 and G8 on formation and trafficking of the G5/G8 heterodimer , mutant forms of the half-transporters were expressed in CHO-K1 cells
- All 13 mutations reduced trafficking of the G5/G8 heterodimer from the endoplasmic reticulum to the Golgi complex, and most prevented the formation of stable heterodimers between G5 and G8
- We conclude that the majority of the molecular defects in G5 and G8 that cause sitosterolemia impair transport of the sterol transporter to the cell surface