Class II histocompatibility molecules associate with calnexin during assembly in the endoplasmic reticulum

Publisher Website
Google Scholar
Abstract
Class II histocompatibility antigens are composed of polymorphic α and β polypeptldes which associate in the endoplasmic reticulum (ER) with a third, non-polymorphic invariant polypeptlde (II). The αβII, complexes are subsequently transported through the Golgl to the endosomes, where the II chain dissociates before the αβ complex Is transported to the cell surface. Results from transport-defective class II expression variant studies suggest that class II intracellular transport Is regulated in multiple intracellular compartments. Consistent with this, a large number of studies have demonstrated that protein folding and/or ollgomertzatlon Is facilitated in the ER by a class of proteins collectively known as molecular chaperones. In this report, we show that the ER-resldent protein calnexin associates with human and murlne class II antigens. Specifically, calnexin associates in the ER with free I, polypeptldes and partially assembled wild-type class II complexes, Including Aα and/or AαII, complexes, as well as with αβ dimers Isolated from class II transport-defective cells. Calnexin also physically associates with αβII, complexes, but not with mature αβ dimers. These results suggest that calnexin may regulate class II intracellular transport by facilitating the production of transport competent molecules out of the ER. In addition, we report that the nucleotlde sequence of the gene encoding murlne calnexin shows a high degree of homology to human IP90 and dog calnexin at both the nucleotlde and deduced amlno acid sequence level. The Isolation of cDNA fragments encoding murlne calnexin will allow us to further evaluate the functional consequences of calnexin–class II interaction.

This publication has 0 references indexed in Scilit: