Gedde-Dahl M, Freisewinkel I, Staschewski M, Schenck K, Koch N, Bakke O
Division of Molecular Cell Biology, Department of Biology, University of Oslo, N-0316 Oslo, Norway.
J Biol Chem. 1997 Mar 28;272(13):8281-7. doi: 10.1074/jbc.272.13.8281.
Invariant chain (Ii) is a transmembrane type II protein that forms a complex with the major histocompatibility complex (MHC) class II molecules in the endoplasmic reticulum (ER). The membrane proximal luminal region of Ii is responsible for the non-covalent association with MHC class II molecules. Chemical cross-linking in COS cells was used to study the effect of luminal and cytoplasmic deletions on trimerization of Ii. We demonstrate that trimerization of Ii is independent of the cytosolic tail of Ii, whereas residues 162-191 (the sequence encoded by exon 6) in the luminal part of Ii are essential for trimer formation. Immunofluorescence studies of the transfected luminal deletion constructs show that the amino acids encoded by exon 6 of Ii are also essential for the induction of large endosomal vesicles. The data suggest that Ii must be in a trimeric form to modify the endosomal pathway.
恒定链（Ii）是一种跨膜II型蛋白，在内质网（ER）中与主要组织相容性复合体（MHC）II类分子形成复合物。Ii的膜近端腔区负责与MHC II类分子的非共价结合。利用COS细胞中的化学交联来研究腔区和胞质区缺失对Ii三聚化的影响。我们证明，Ii的三聚化不依赖于Ii的胞质尾，而Ii腔区的162 - 191位残基（由外显子6编码的序列）对于三聚体形成至关重要。对转染的腔区缺失构建体的免疫荧光研究表明，Ii外显子6编码的氨基酸对于诱导大内体囊泡也至关重要。数据表明，Ii必须以三聚体形式才能修饰内体途径。
