Chamberlain L H, Burgoyne R D
The Physiological Laboratory, University of Liverpool, Crown Street, Liverpool L69 3BX, UK.
Biochem J. 1998 Oct 15;335 ( Pt 2)(Pt 2):205-9. doi: 10.1042/bj3350205.
The post-translational addition of palmitic acid residues to cysteine-string protein (Csp) was originally thought to form the basis for membrane association of this secretory-vesicle protein. However, subsequent work showed that chemical depalmitoylation of Csp does not result in its release from membranes. We have confirmed these findings and employed [3H]palmitate labelling of PC12 cells to demonstrate that Csp1 remains associated with membranes following the complete removal of palmitic acid residues. Although palmitoylation is not essential for the stable membrane association of Csp, its role in membrane targeting has not been assessed. To examine this, we constructed a Csp mutant protein with seven cysteines replaced by serines in the cysteine-string domain. In contrast to wild-type Csps, this mutant protein was not targeted to membranes when expressed in PC12 or HeLa cells. We conclude that although a palmitoylated cysteine-string domain is not required for stable membrane association of Csp, it is essential for initial membrane targeting.
最初认为，在翻译后将棕榈酸残基添加到半胱氨酸串蛋白（Csp）上，构成了这种分泌囊泡蛋白与膜结合的基础。然而，随后的研究表明，对Csp进行化学去棕榈酰化处理并不会使其从膜上释放。我们证实了这些发现，并利用[3H]棕榈酸对PC12细胞进行标记，以证明在棕榈酸残基完全去除后，Csp1仍与膜结合。虽然棕榈酰化对于Csp与膜的稳定结合并非必不可少，但其在膜靶向中的作用尚未得到评估。为了对此进行研究，我们构建了一种Csp突变蛋白，其半胱氨酸串结构域中的7个半胱氨酸被丝氨酸取代。与野生型Csp不同，这种突变蛋白在PC12或HeLa细胞中表达时不会靶向到膜上。我们得出结论，虽然棕榈酰化的半胱氨酸串结构域对于Csp与膜的稳定结合并非必需，但它对于初始膜靶向至关重要。
