title: The cytosolic chaperone α-crystallin B rescues folding and compartmentalization of misfolded multispan transmembrane proteins.
abstract: The α-crystallin B chain (CRYAB or HspB5) is a cytosolic chaperone belonging to the small heat shock protein family, which is known to help in the folding of cytosolic proteins. Here we show that CRYAB binds the mutant form of at least two multispan transmembrane proteins (TMPs), exerting an anti-aggregation activity. It rescues the folding of mutant Frizzled4, which is responsible for a rare autosomal dominant form of familial exudative vitreoretinopathy (Fz4-FEVR), and the mutant ATP7B Cu transporter (ATP7B-H1069Q) associated with a common form of Wilson's disease. In the case of Fz4-FEVR, CRYAB prevents the formation of inter-chain disulfide bridges between the lumenal ectodomains of the aggregated mutant chains, which enables correct folding and promotes appropriate compartmentalization on the plasma membrane. ATP7B-H1069Q, with help from CRYAB, folds into the proper conformation, moves to the Golgi complex, and responds to copper overload in the same manner as wild-type ATP7B. These findings strongly suggest that CRYAB plays a pivotal role, previously undetected, in the folding of multispan TMPs and, from the cytosol, is able to orchestrate folding events that take place in the lumen of the ER. Our results contribute to the explanation of the complex scenario behind multispan TMP folding; additionally, they serve to expose interesting avenues for novel therapeutic approaches.
authors.affiliation: Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, 80131 Naples, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: D'Agostino
authors.forename: Valentina
authors.initials: V
authors.lastname: Lemma
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Chesi
authors.forename: Mariano
authors.initials: M
authors.lastname: Stornaiuolo
authors.forename: Magda
authors.initials: M
authors.lastname: Cannata Serio
authors.forename: Chiara
authors.initials: C
authors.lastname: D'Ambrosio
authors.forename: Andrea
authors.initials: A
authors.lastname: Scaloni
authors.forename: Roman
authors.initials: R
authors.lastname: Polishchuk
authors.forename: Stefano
authors.initials: S
authors.lastname: Bonatti
mesh_terms: D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics*; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D014162:Transfection; D038203:alpha-Crystallin B Chain / Q000737:chemistry* / Q000502:physiology
chemical_list: D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D038203:alpha-Crystallin B Chain
keywords: ATP7B; Frizzled4; sHsp