Sousa M C, Parodi A J
Instituto de Investigaciones Bioquímicas Fundación Campomar, Buenos Aires, Argentina.
Cell Mol Biol (Noisy-le-grand). 1996 Jul;42(5):609-16.
The UDP-Glyc:glycoprotein glucosyltransferase is a soluble protein of the endoplasmic reticulum that in cell-free assays glucosylates denatured but not native glycoproteins. It has been postulated that the enzyme participates in the quality control mechanism of glycoprotein folding in the endoplasmic reticulum by which only properly folded species are transported to the Golgi apparatus. This paper reports studies on the protein determinants that upon recognition by the glucosyltransferase allow the selective glucosylation of denatured glycoproteins. It is shown here that extensive chemical modification of denatured soybean agglutinin does not modify its glucose acceptor capacity, thus suggesting that the protein determinants recognized by the glucosyltransferase are not formed by specific amino acids. Moreover, it is reported that the enzyme binds patches of hydrophobic amino acids exposed in denatured but not in native conformations. As exposure of such residues is the only feature common to all misfolded conformations, it is suggested that binding to hydrophobic amino acids forms part of the recognition mechanism of denatured conformations by the glucosyltransferase.
UDP-糖：糖蛋白葡糖基转移酶是一种内质网可溶性蛋白，在无细胞分析中，它能使变性糖蛋白而非天然糖蛋白发生葡糖基化。据推测，该酶参与内质网中糖蛋白折叠的质量控制机制，通过这一机制，只有正确折叠的糖蛋白才能被转运至高尔基体。本文报道了关于蛋白质决定簇的研究，葡糖基转移酶识别这些决定簇后，可使变性糖蛋白发生选择性葡糖基化。本文表明，对变性大豆凝集素进行广泛的化学修饰不会改变其葡萄糖受体能力，因此表明葡糖基转移酶识别的蛋白质决定簇并非由特定氨基酸形成。此外，据报道，该酶能结合在变性而非天然构象中暴露的疏水性氨基酸区域。由于此类残基的暴露是所有错误折叠构象共有的唯一特征，因此有人提出，与疏水性氨基酸的结合是葡糖基转移酶识别变性构象机制的一部分。
