Jacobsen L, Madsen P, Jacobsen C, Nielsen M S, Gliemann J, Petersen C M
Department of Medical Biochemistry, University of Aarhus, DK-8000, Aarhus C, Denmark.
J Biol Chem. 2001 Jun 22;276(25):22788-96. doi: 10.1074/jbc.M100857200. Epub 2001 Apr 9.
We previously isolated and sequenced the approximately 250-kDa type 1 receptor sorLA/LR11, a mosaic protein with elements characterizing the Vps10p domain receptor family as well as the low density lipoprotein receptor family. The N terminus of the Vps10p domain comprises a consensus sequence for cleavage by furin ((50)RRKR(53)) that precedes a truncation found in sorLA isolated from human brain. Here we show that sorLA, like sortilin-1/neurotensin receptor-3, whose lumenal domain consists of a Vps10p domain only, is synthesized as a proreceptor that is cleaved by furin in late Golgi compartments. We show that the truncation conditions the Vps10p domain for propeptide inhibitable binding of neuropeptides and the receptor-associated protein. We further demonstrate that avid binding of the receptor-associated protein, apolipoprotein E, and lipoprotein lipase not inhibited by propeptide occurs to sites located in other lumenal domains. In transfected cells, about 10% of full-length sorLA were expressed on the cell surface capable of mediating endocytosis. However, the major pool of receptors was found in late Golgi compartments, suggesting possible interaction with newly synthesized ligands. The results show that sorLA, following activation by truncation, binds multiple ligands and may mediate both endocytosis and sorting.
我们之前分离并测序了约250 kDa的1型受体sorLA/LR11，它是一种镶嵌蛋白，兼具Vps10p结构域受体家族以及低密度脂蛋白受体家族的特征元件。Vps10p结构域的N端包含一个由弗林蛋白酶切割的共有序列（(50)RRKR(53)），该序列在从人脑分离的sorLA中发现的截短之前。在这里我们表明，sorLA与sortilin-1/神经降压素受体-3一样，其腔内结构域仅由一个Vps10p结构域组成，它作为一种前体受体合成，在高尔基体晚期被弗林蛋白酶切割。我们表明，这种截短使Vps10p结构域能够与神经肽和受体相关蛋白进行前肽可抑制性结合。我们进一步证明，受体相关蛋白、载脂蛋白E和脂蛋白脂肪酶的avid结合（不受前肽抑制）发生在其他腔内结构域的位点。在转染细胞中，约10%的全长sorLA在能够介导内吞作用的细胞表面表达。然而，主要的受体池存在于高尔基体晚期，提示可能与新合成的配体相互作用。结果表明，sorLA在被截短激活后，能结合多种配体，并可能介导内吞作用和分选。
