Ca2+-mediated higher-order assembly of heterodimers in amino acid transport system b0,+ biogenesis and cystinuria

• Published in: Nature communications 2022-05, Vol.13 (1), p.2708-2708, Article 2708
• Main Authors: Lee, Yongchan, Wiriyasermkul, Pattama, Kongpracha, Pornparn, Moriyama, Satomi, Mills, Deryck J., Kühlbrandt, Werner, Nagamori, Shushi
• Format: Article
• Language: English
• Subjects: 101/28; 14/19; 631/45/221; 631/45/470/1463; 631/535/1258/1259; 631/80/313/1463; 692/699/317; 82/29; Amino acids; Assembly; Biosynthesis; Calcium; Calcium ions; Calculi; Cystinuria; Dimerization; Evolution; Genetic disorders; Glycan; Glycoproteins; Humanities and Social Sciences; Inactivation; Kidneys; Maturation; multidisciplinary; Mutation; Nephrolithiasis; Phenotypes; Protein transport; Proteins; Regulatory subunits; Renal failure; Science; Science (multidisciplinary); Transportation systems
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-30293-9

Cystinuria is a genetic disorder characterized by overexcretion of dibasic amino acids and cystine, causing recurrent kidney stones and kidney failure. Mutations of the regulatory glycoprotein rBAT and the amino acid transporter b 0,+ AT, which constitute system b 0,+ , are linked to type I and non-type I cystinuria respectively and they exhibit distinct phenotypes due to protein trafficking defects or catalytic inactivation. Here, using electron cryo-microscopy and biochemistry, we discover that Ca 2+ mediates higher-order assembly of system b 0,+ . Ca 2+ stabilizes the interface between two rBAT molecules, leading to super-dimerization of b 0,+ AT–rBAT, which in turn facilitates N-glycan maturation and protein trafficking. A cystinuria mutant T216M and mutations of the Ca 2+ site of rBAT cause the loss of higher-order assemblies, resulting in protein trapping at the ER and the loss of function. These results provide the molecular basis of system b 0,+ biogenesis and type I cystinuria and serve as a guide to develop new therapeutic strategies against it. More broadly, our findings reveal an unprecedented link between transporter oligomeric assembly and protein-trafficking diseases. Cystinuria is caused by mutations in heterodimeric amino acid transporter known as system b 0,+ . Here, authors discover that Ca 2+ stabilizes the interface between two system b 0,+ regulatory subunits rBAT, leading to super-dimerization of the b 0,+ AT–rBAT heterodimer, facilitating system b 0,+ maturation.