Defective intracellular transport and processing of OA1 is a major cause of ocular albinism type 1

• Published in: Human molecular genetics Vol. 9; no. 20; pp. 3011 - 3018
• Main Authors: D'ADDIO, Marilena, PIZZIGONI, Alessandro, BASSI, Maria Teresa, BASCHIROTTO, Cinzia, VALETTI, Caterina, INCERTI, Barbara, CLEMENTI, Maurizio, DE LUCA, Michele, BALLABIO, Andrea, SCHIAFFINO, Maria Vittoria
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 12-12-2000; Oxford Publishing Limited (England)
• Subjects: Albinism, Ocular - genetics; Albinism, Ocular - metabolism; Amino Acid Sequence; Animals; Biological and medical sciences; Biological Transport; Blotting, Western; Cells, Cultured; COS Cells; Dermatology; Eye Proteins - chemistry; Eye Proteins - genetics; Eye Proteins - metabolism; Fluorescent Antibody Technique; Glycosylation; Golgi Apparatus - metabolism; Humans; Medical sciences; Melanocytes - physiology; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation, Missense; Pigmentary diseases of the skin; Protein Conformation; Human; Intracellular transport; Skin disease; Melatonin; Pigmentation disorder; Molecular processing; Albinism; Ocular; Metabolic diseases; Uvea disease; Enzymopathy; Structure function relationship; Genetic disease; Eye disease; Mutation; Localization; Aminoacid disorder; G protein; Biological receptor
• ISSN: 0964-6906; 1460-2083; 1460-2083
• DOI: 10.1093/hmg/9.20.3011

Ocular albinism type 1 (OA1) is an X-linked disorder mainly characterized by a severe reduction of visual acuity, hypopigmentation of the retina and the presence of macromelanosomes in the skin and eyes. Various types of mutation have been identified within the OA1 gene in patients with the disorder, including several missense mutations of unknown functional significance. In order to shed light into the molecular pathogenesis of ocular albinism and possibly define critical functional domains within the OA1 protein, we characterized 19 independent missense mutations with respect to processing and subcellular distribution on expression in COS-7 cells. Our analysis indicates the presence of at least two distinct biochemical defects associated with the different missense mutations. Eleven of the nineteen OA1 mutants (approximately 60%) were retained in the endoplasmic reticulum, showing defecNStive intracellular transport and glycosylation, consistent with protein misfolding. The remaining eight of the nineteen OA1 mutants (approximately 40%) displayed sorting and processing behaviours indistinguishable from those of the wild-type protein. Consistent with our recent findings that OA1 represents a novel type of intracellular G protein-coupled receptor (GPCR), we found that most of these latter mutations cluster within the second and third cytosolic loops, two regions that in canonical GPCRs are known to be critical for their downstream signaling, including G protein-coupling and effector activation. The biochemical analysis of OA1 mutations performed in this study provides important insights into the structure-function relationships of the OA1 protein and implies protein misfolding as a major pathogenic mechanism in OA1.