Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia.
J Cell Sci. 2010 Feb 15;123(Pt 4):544-54. doi: 10.1242/jcs.059097. Epub 2010 Jan 19.
Eukaryotic flagella and cilia are surrounded by a membrane that is continuous with, but distinct from, the rest of the plasma membrane. In Leishmania parasites, the inner leaflet of the flagellar membrane is coated with the acylated membrane protein, SMP-1. Here, we provide evidence that SMP-1 stabilizes the flagellar membrane and is required for flagella elongation and function. The expression and flagella targeting of SMP-1 is tightly associated with flagella elongation during amastigote to promastigote differentiation. Deletion of the genes encoding SMP-1 and the flagellar pocket protein SMP-2, led to the production of short flagella and defects in motility. Alterations in the physical properties of the smp-1/smp-2(-/-) flagellar membrane were suggested by: (1) the accumulation of membrane vesicles in the flagellar matrix, and (2) further retraction of flagella following partial inhibition of sterol and sphingolipid biosynthesis. The flagella phenotype of the smp-1/smp-2(-/-) null mutant was reversed by re-expression of SMP-1, but not SMP-2. SMP-1 contains a jelly-roll beta-sheet structure that is probably conserved in all SMP proteins, and forms stable homo-oligomers in vivo. We propose that the SMP-1 coat generates and/or stabilizes sterol- and sphingolipid-rich domains in the flagellar membrane.
真核鞭毛和纤毛被一层膜包围，该膜与质膜的其余部分连续但又不同。在利什曼原虫寄生虫中，鞭毛膜的内小叶涂覆有酰化膜蛋白 SMP-1。在这里，我们提供的证据表明 SMP-1 稳定了鞭毛膜，并需要鞭毛伸长和功能。SMP-1 的表达和鞭毛靶向与无鞭毛体向前鞭毛体分化过程中的鞭毛伸长紧密相关。编码 SMP-1 和鞭毛口袋蛋白 SMP-2 的基因缺失导致短鞭毛的产生和运动缺陷。smp-1/smp-2(-/-)鞭毛膜物理性质的改变表明：（1）在鞭毛基质中积累膜泡，以及（2）在固醇和鞘脂生物合成部分抑制后进一步缩回鞭毛。smp-1/smp-2(-/-) 缺失突变体的鞭毛表型通过重新表达 SMP-1 而不是 SMP-2 得到逆转。SMP-1 含有一个果冻卷 β-折叠结构，可能在所有 SMP 蛋白中都保守，并在体内形成稳定的同源寡聚体。我们提出，SMP-1 涂层在鞭毛膜中产生和/或稳定固醇和鞘脂丰富的区域。
