title: A role for calnexin (IP90) in the assembly of class II MHC molecules.
abstract: Major histocompatibility complex (MHC) class II antigens consist of alpha and beta chains that associate intracellularly with the invariant (I) chain. The HLA-DR alpha beta I complex assembles in the endoplasmic reticulum (ER) into a nonameric structure via progressive addition of three alpha beta dimers to a core invariant chain trimer. We have examined intracellular association of alpha beta I complexes with the resident ER protein calnexin. Calnexin associates rapidly (within 3 min) with newly synthesized alpha, beta and I chains, and remains associated with the assembling alpha beta I complex until the final alpha beta dimer is added, forming the complete nonamer. Dissociation of calnexin parallels egress of alpha beta I from the ER. These results suggest that calnexin retains and stabilizes both free class II subunits and partially assembled class II-I chain complexes until assembly of the nonamer is complete.
authors.affiliation: Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510.
authors.forename: K S
authors.initials: KS
authors.lastname: Anderson
authors.forename: P
authors.initials: P
authors.lastname: Cresswell
mesh_terms: D002135:Calcium-Binding Proteins / Q000378:metabolism*; D037281:Calnexin; D015180:Electrophoresis, Gel, Two-Dimensional; D006367:HeLa Cells; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans
chemical_list: D002135:Calcium-Binding Proteins; D000949:Histocompatibility Antigens Class II; D037281:Calnexin