Gorlin J B, Yamin R, Egan S, Stewart M, Stossel T P, Kwiatkowski D J, Hartwig J H
Department of Medicine, Massachusetts General Hospital, Charlestown.
J Cell Biol. 1990 Sep;111(3):1089-105. doi: 10.1083/jcb.111.3.1089.
Actin-binding protein (ABP-280, nonmuscle filamin) is a ubiquitous dimeric actin cross-linking phosphoprotein of peripheral cytoplasm, where it promotes orthogonal branching of actin filaments and links actin filaments to membrane glycoproteins. The complete nucleotide sequence of human endothelial cell ABP cDNA predicts a polypeptide subunit chain of 2,647 amino acids, corresponding to 280 kD, also the mass derived from physical measurements of the native protein. The actin-binding domain is near the amino-terminus of the subunit where the amino acid sequence is similar to other actin filament binding proteins, including alpha-actinin, beta-spectrin, dystrophin, and Dictyostelium abp-120. The remaining 90% of the sequence comprises 24 repeats, each approximately 96 residues long, predicted to have stretches of beta-sheet secondary structure interspersed with turns. The first 15 repeats may have substantial intrachain hydrophobic interactions and overlap in a staggered fashion to yield a backbone with mechanical resilience. Sequence insertions immediately before repeats 16 and 24 predict two hinges in the molecule near points where rotary-shadowed molecules appear to swivel in electron micrographs. Both putative hinge regions are susceptible to cleavage by proteases and the second also contains the site that binds the platelet glycoprotein Ib/IX complex. Phosphorylation consensus sequences are also located in the hinges or near them. Degeneracy within every even-numbered repeat between 16 and 24 and the insertion before repeat 24 may convert interactions within chains to interactions between chains to account for dimer formation within a domain of 7 kD at the carboxy-terminus. The structure of ABP dimers resembles a leaf spring. Interchain interactions hold the leaves firmly together at one end, whereas intrachain hydrophobic bonds reinforce the arms of the spring where the leaves diverge, making it sufficiently stiff to promote high-angle branching of actin filaments. The large size of the leaves, their interruption by two hinges and flexible actin-binding site, facilitate cross-linking of widely dispersed actin filaments.
肌动蛋白结合蛋白（ABP - 280，非肌肉细丝蛋白）是一种存在于外周细胞质中的普遍存在的二聚体肌动蛋白交联磷蛋白，在那里它促进肌动蛋白丝的正交分支，并将肌动蛋白丝与膜糖蛋白连接起来。人内皮细胞ABP cDNA的完整核苷酸序列预测有一个由2647个氨基酸组成的多肽亚基链，对应于280 kD，这也是天然蛋白质物理测量得出的质量。肌动蛋白结合结构域靠近亚基的氨基末端，其氨基酸序列与其他肌动蛋白丝结合蛋白相似，包括α - 辅肌动蛋白、β - 血影蛋白、肌营养不良蛋白和盘基网柄菌abp - 120。其余90%的序列由24个重复序列组成，每个重复序列大约96个残基长，预计具有穿插着转角的β - 折叠二级结构片段。前15个重复序列可能有大量链内疏水相互作用，并以交错方式重叠，形成具有机械弹性的主链。在重复序列16和24之前的序列插入预测分子中有两个铰链，靠近旋转阴影分子在电子显微镜下似乎旋转的点。两个假定的铰链区域都易被蛋白酶切割，第二个铰链区域还包含与血小板糖蛋白Ib/IX复合物结合的位点。磷酸化共有序列也位于铰链处或其附近。16到24之间每个偶数重复序列内的简并性以及重复序列24之前的插入可能将链内相互作用转化为链间相互作用，以解释羧基末端7 kD结构域内的二聚体形成。ABP二聚体的结构类似于板簧。链间相互作用在一端将叶片牢固地结合在一起，而链内疏水键加强了叶片分开处的弹簧臂，使其足够坚硬以促进肌动蛋白丝的高角度分支。叶片的大尺寸、被两个铰链和灵活的肌动蛋白结合位点中断，有利于广泛分散的肌动蛋白丝的交联。
