Panic Bojana, Whyte James R C, Munro Sean
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom.
Curr Biol. 2003 Mar 4;13(5):405-10. doi: 10.1016/s0960-9822(03)00091-5.
The ARLs are a diverse family of GTPases that are related to ADP-ribosylation factors (ARFs), but whose function is poorly understood. There are at least ten ARLs in humans, two of which have homologs in the yeast Saccharomyces cerevisiae (ARL1/Arl1p and ARFRP1/Arl3p). The function of ARFRP1 is unknown, but mammalian ARL1 has recently been found to interact with a number of effectors including the GRIP domain that is present in a family of Golgi-localized long coiled-coil proteins. We find that in yeast, the intracellular targeting of Imh1p, the only yeast GRIP domain protein, is dependent on both Arl1p and Arl3p, but not on the ARF proteins. A recombinant form of the Imh1p GRIP domain binds to Arl1p in a GTP-dependent manner, but not to Arl3p. Yeast also contain a relative of SCOCO, a protein proposed to bind human ARL1, but this yeast protein, Slo1p, appears to bind Arl3p rather than Arl1p in vitro. However, Imh1p is not the sole effector of Arl1p since affinity chromatography of cytosol with immobilized Arl1p:GTP revealed an interaction with the GARP/VFT complex that is thought to act in the tethering of vesicles to the Golgi apparatus. Finally, we find that Arl3p is required in vivo for the targeting of Arl1p, explaining its requirement for the normal distribution of Imh1p.
ARL蛋白是一类多样的GTP酶家族,与ADP核糖基化因子(ARF)相关,但其功能却鲜为人知。人类中至少有十种ARL蛋白,其中两种在酿酒酵母中有同源物(ARL1/Arl1p和ARFRP1/Arl3p)。ARFRP1的功能尚不清楚,但最近发现哺乳动物的ARL1与许多效应蛋白相互作用,包括存在于高尔基定位的长卷曲螺旋蛋白家族中的GRIP结构域。我们发现在酵母中,唯一的酵母GRIP结构域蛋白Imh1p的细胞内靶向依赖于Arl1p和Arl3p,但不依赖于ARF蛋白。Imh1p GRIP结构域的重组形式以GTP依赖的方式与Arl1p结合,但不与Arl3p结合。酵母中还含有SCOCO的一个相关蛋白,该蛋白被认为可结合人类ARL1,但这种酵母蛋白Slo1p在体外似乎结合Arl3p而非Arl1p。然而,Imh1p不是Arl1p的唯一效应蛋白,因为用固定化的Arl1p:GTP对细胞质进行亲和层析显示它与GARP/VFT复合物存在相互作用,该复合物被认为在囊泡与高尔基体的拴系中起作用。最后,我们发现在体内Arl3p是Arl1p靶向所必需的,这解释了它对Imh1p正常分布的必要性。