The calponin family proteins are expressed in both muscle and non-muscle cells and involved in the regulation of cytoskeletal dynamics and cell contractility. In the nematode Caenorhabditis elegans, UNC-87 and CLIK-1 are calponin-related proteins with 42% identical amino acid sequences containing seven calponin-like motifs. Genetic studies demonstrated that UNC-87 and CLIK-1 have partially redundant function in regulating actin cytoskeletal organization in striated and non-striated muscle cells. However, biochemical studies showed that UNC-87 and CLIK-1 are different in their ability to bundle actin filaments. In this study, I extended comparison between UNC-87 and CLIK-1 and found additional differences in vitro and in vivo. Although UNC-87 and CLIK-1 bound to actin filaments similarly, UNC-87, but not CLIK-1, bound to myosin and inhibited actomyosin ATPase in vitro. In striated muscle, UNC-87 and CLIK-1 were segregated into different subregions within sarcomeric actin filaments. CLIK-1 was concentrated near the actin pointed ends, whereas UNC-87 was enriched toward the actin barbed ends. Restricted localization of UNC-87 was not altered in a clik-1-null mutant, suggesting that their segregated localization is not due to competition between the two related proteins. These results suggest that the two calponin-related proteins have both common and distinct roles in regulating actin filaments.

中文翻译：

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秀丽隐杆线虫横纹肌肌节细丝内两种钙调蛋白相关蛋白的分离定位

钙调蛋白家族蛋白在肌肉和非肌肉细胞中表达，并参与细胞骨架动力学和细胞收缩性的调节。在线虫秀丽隐杆线虫中，UNC-87 和 CLIK-1 是钙调蛋白相关蛋白，具有 42% 的相同氨基酸序列，包含 7 个钙调蛋白样基序。遗传学研究表明，UNC-87 和 CLIK-1 在调节横纹肌细胞和非横纹肌细胞中的肌动蛋白细胞骨架组织方面具有部分冗余的功能。然而，生化研究表明 UNC-87 和 CLIK-1 捆绑肌动蛋白丝的能力不同。在这项研究中，我扩展了 UNC-87 和 CLIK-1 之间的比较，发现了体外和体内的其他差异。尽管UNC-87和CLIK-1与肌动蛋白丝的结合类似，但UNC-87而非CLIK-1在体外与肌球蛋白结合并抑制肌动球蛋白ATP酶。在横纹肌中，UNC-87 和 CLIK-1 被分离到肌节肌动蛋白丝内的不同亚区域。 CLIK-1 集中在肌动蛋白尖端附近，而 UNC-87 则集中在肌动蛋白带刺末端附近。 UNC-87 的限制性定位在clik-1- null 突变体中没有改变，表明它们的分离定位不是由于两种相关蛋白之间的竞争。这些结果表明，两种钙调蛋白相关蛋白在调节肌动蛋白丝方面具有共同和不同的作用。