Loomis Patricia A, Zheng Lili, Sekerková Gabriella, Changyaleket Benjarat, Mugnaini Enrico, Bartles James R
Department of Cell and Molecular Biology, Feinberg School of Medicine, Institute of Neuroscience, Northwestern University, 303 East Chicago Ave., Chicago, IL 60611, USA.
J Cell Biol. 2003 Dec 8;163(5):1045-55. doi: 10.1083/jcb.200309093. Epub 2003 Dec 1.
The espin actin-bundling proteins, which are the target of the jerker deafness mutation, caused a dramatic, concentration-dependent lengthening of LLC-PK1-CL4 cell microvilli and their parallel actin bundles. Espin level was also positively correlated with stereocilium length in hair cells. Villin, but not fascin or fimbrin, also produced noticeable lengthening. The espin COOH-terminal peptide, which contains the actin-bundling module, was necessary and sufficient for lengthening. Lengthening was blocked by 100 nM cytochalasin D. Espin cross-links slowed actin depolymerization in vitro less than twofold. Elimination of an actin monomer-binding WASP homology 2 domain and a profilin-binding proline-rich domain from espin did not decrease lengthening, but made it possible to demonstrate that actin incorporation was restricted to the microvillar tip and that bundles continued to undergo actin treadmilling at approximately 1.5 s-1 during and after lengthening. Thus, through relatively subtle effects on actin polymerization/depolymerization reactions in a treadmilling parallel actin bundle, espin cross-links cause pronounced barbed-end elongation and, thereby, make a longer bundle without joining shorter modules.
埃斯平肌动蛋白成束蛋白是震颤性耳聋突变的靶点，它会导致LLC-PK1-CL4细胞微绒毛及其平行肌动蛋白束显著地、浓度依赖性地延长。埃斯平水平也与毛细胞中静纤毛的长度呈正相关。绒毛蛋白而非细丝蛋白或丝束蛋白也会产生明显的延长。包含肌动蛋白成束模块的埃斯平COOH末端肽对于延长是必要且充分的。100 nM的细胞松弛素D可阻断延长。埃斯平交联在体外使肌动蛋白解聚减慢不到两倍。从埃斯平中去除肌动蛋白单体结合的WASP同源2结构域和富含脯氨酸的脯肌动蛋白结合结构域不会减少延长，但能够证明肌动蛋白的掺入仅限于微绒毛尖端，并且在延长期间和延长后，肌动蛋白束以约1.5 s-1的速度继续进行肌动蛋白踏车运动。因此，通过对踏车运动的平行肌动蛋白束中的肌动蛋白聚合/解聚反应产生相对微妙的影响，埃斯平交联导致明显的带刺末端伸长，从而形成更长的束而无需连接较短的模块。
