The Ronald O Perelman Department of Dermatology, New York University Grossman School of Medicine, New York, NY, USA
The Perlmutter Cancer Center, New York University Langone Medical Center, New York, NY, USA.
Life Sci Alliance. 2021 Feb 12;4(5). doi: 10.26508/lsa.202000972. Print 2021 May.
Isoprenylcysteine carboxyl methyltransferase (ICMT) is the third of three enzymes that sequentially modify the C-terminus of CaaX proteins, including RAS. Although all four RAS proteins are substrates for ICMT, each traffics to membranes differently by virtue of their hypervariable regions that are differentially palmitoylated. We found that among RAS proteins, NRAS was unique in requiring ICMT for delivery to the PM, a consequence of having only a single palmitoylation site as its secondary affinity module. Although not absolutely required for palmitoylation, acylation was diminished in the absence of ICMT. Photoactivation and FRAP of GFP-NRAS revealed increase flux at the Golgi, independent of palmitoylation, in the absence of ICMT. Association of NRAS with the prenyl-protein chaperone PDE6δ also required ICMT and promoted anterograde trafficking from the Golgi. We conclude that carboxyl methylation of NRAS is required for efficient palmitoylation, PDE6δ binding, and homeostatic flux through the Golgi, processes that direct delivery to the plasma membrane.
异戊烯基半胱氨酸羧基甲基转移酶（ICMT）是顺序修饰 CaaX 蛋白 C 端的三种酶中的第三种，包括 RAS。尽管所有四种 RAS 蛋白都是 ICMT 的底物，但由于它们的超可变区具有不同的棕榈酰化，每种蛋白都通过不同的方式运输到膜上。我们发现，在 RAS 蛋白中，NRAS 是唯一需要 ICMT 才能递送到质膜的蛋白，这是因为它只有一个单一的棕榈酰化位点作为其二级亲和模块。尽管不是棕榈酰化的绝对要求，但在没有 ICMT 的情况下，酰化作用减少。GFP-NRAS 的光激活和 FRAP 显示，在没有 ICMT 的情况下，高尔基体的通量增加，与棕榈酰化无关。NRAS 与prenyl-protein chaperone PDE6δ 的结合也需要 ICMT，并促进从高尔基体的正向运输。我们得出结论，NRAS 的羧基甲基化是有效棕榈酰化、PDE6δ 结合和通过高尔基体的稳态通量所必需的，这些过程指导递送到质膜。
