Azim A C, Knoll J H, Beggs A H, Chishti A H
Department of Biomedical Research, St. Elizabeth's Medical Center, Tufts University School of Medicine, Boston, Massachusetts 02135, USA.
J Biol Chem. 1995 Jul 21;270(29):17407-13. doi: 10.1074/jbc.270.29.17407.
Dematin is an actin-bundling protein of the erythroid membrane skeleton and is abundantly expressed in human brain, heart, skeletal, muscle, kidney, and lung. The 48-kDa subunit of dematin contains a headpiece domain which was originally identified in villin, and actin-binding protein of the brush-border cytoskeleton. The head-piece domain of villin is essential for its morphogenic function in vivo. Here we report the primary structure of 52-kDa subunit of dematin which differs from the 48-kDa subunit by a 22-amino-acid insertion within its headpiece domain. A unique feature of the insertion sequence of the 52-kDa subunit is its homology to erythrocyte protein 4.2. The insertion sequence also includes a cysteine residue which may explain the formation of sulfhydryl-linked trimers of dematin. Actin binding measurements using recombinant fusion proteins revealed that each monomer of dematin contains two F-actin binding sites: one in the headpiece domain and the other in the undefined N-terminal domain. Although the actin bundling activity of intact dematin was abolished by phosphorylation, no effect of phosphorylation was observed on the actin binding activity of fusion proteins. Using somatic cell hybrid panels and fluorescence in situ hybridization, the dematin gene was localized on the short arm of chromosome 8. The dematin locus, 8p21.1, is distal to the known locus of human erythroid ankyrin (8p11.2) and may contribute to the etiology of hemolytic anemia in a subset of patients with severe hereditary spherocytosis.
肌动蛋白结合蛋白是红细胞膜骨架中的一种肌动蛋白成束蛋白，在人类大脑、心脏、骨骼、肌肉、肾脏和肺中大量表达。肌动蛋白结合蛋白的48 kDa亚基包含一个头部结构域，该结构域最初是在绒毛蛋白（刷状缘细胞骨架的一种肌动蛋白结合蛋白）中发现的。绒毛蛋白的头部结构域对其在体内的形态发生功能至关重要。在此，我们报告了肌动蛋白结合蛋白52 kDa亚基的一级结构，它与48 kDa亚基的区别在于其头部结构域内有一个22个氨基酸的插入序列。52 kDa亚基插入序列的一个独特特征是它与红细胞蛋白4.2具有同源性。插入序列还包括一个半胱氨酸残基，这可能解释了肌动蛋白结合蛋白巯基连接三聚体的形成。使用重组融合蛋白进行的肌动蛋白结合测量表明，肌动蛋白结合蛋白的每个单体包含两个F-肌动蛋白结合位点：一个在头部结构域，另一个在未明确的N端结构域。尽管完整的肌动蛋白结合蛋白的肌动蛋白成束活性因磷酸化而被消除，但未观察到磷酸化对融合蛋白的肌动蛋白结合活性有影响。利用体细胞杂交板和荧光原位杂交技术，将肌动蛋白结合蛋白基因定位在8号染色体的短臂上。肌动蛋白结合蛋白基因座8p21.1位于人类红细胞锚蛋白已知基因座（8p11.2）的远端，可能在一部分严重遗传性球形红细胞增多症患者的溶血性贫血病因中起作用。
