Ashford D A, Alafi C D, Gamble V M, Mackay D J, Rademacher T W, Williams P J, Dwek R A, Barclay A N, Davis S J, Somoza C
Department of Biochemistry, Sir William Dunn School of Pathology, University of Oxford, United Kingdom.
J Biol Chem. 1993 Feb 15;268(5):3260-7.
The rat and human forms of the T-cell surface glycoprotein CD4 share a common glycosylation site at the Asn270/271 position but differ with respect to the locations of the second glycosylation sites at Asn159 (rat) and Asn300 (human). The glycosylation of soluble recombinant forms of human and rat CD4 (sCD4) expressed in Chinese hamster ovary cells has been characterized. The most obvious differences between the rat and human sCD4 oligosaccharides were the greater abundance of oligomannose and hybrid oligosaccharides on rat sCD4 and the presence of oligosaccharides carrying a terminal alpha-galactose residue on human sCD4. This is the first report of the occurrence of alpha-galactose residues on a glycoprotein expressed in Chinese hamster ovary cells. Comparison of mutant rat sCD4 molecules with single glycosylation sites and glycopeptides indicated that site-specific and independent processing occurred at each glycosylation site. The glycosylation at the conserved site at Asn270 of rat sCD4 was identical to that seen for the equivalent site in human sCD4, and the oligomannose and hybrid structures were restricted to the nonconserved site at Asn159 in rat sCD4. However, there was more oligosaccharide processing at this site in a truncated form of rat sCD4 consisting of the two NH2-terminal domains. These results indicate that not only the local three-dimensional structure but also domain interactions can influence the processing at individual glycosylation sites.
T细胞表面糖蛋白CD4的大鼠和人类形式在天冬酰胺270/271位置共享一个共同的糖基化位点，但在天冬酰胺159（大鼠）和天冬酰胺300（人类）处的第二个糖基化位点位置不同。已对在中国仓鼠卵巢细胞中表达的人类和大鼠CD4（sCD4）的可溶性重组形式的糖基化进行了表征。大鼠和人类sCD4寡糖之间最明显的差异是大鼠sCD4上的低聚甘露糖和杂合寡糖丰度更高，以及人类sCD4上存在带有末端α-半乳糖残基的寡糖。这是关于在中国仓鼠卵巢细胞中表达的糖蛋白上出现α-半乳糖残基的首次报道。对具有单个糖基化位点的突变大鼠sCD4分子和糖肽的比较表明，每个糖基化位点发生了位点特异性和独立的加工。大鼠sCD4天冬酰胺270保守位点的糖基化与人类sCD4中相应位点的糖基化相同，并且低聚甘露糖和杂合结构仅限于大鼠sCD4中天冬酰胺159的非保守位点。然而，在由两个NH2末端结构域组成的大鼠sCD4截短形式中，该位点有更多的寡糖加工。这些结果表明，不仅局部三维结构，而且结构域相互作用都可以影响单个糖基化位点的加工。
