STRUCTURE OF MACROPHAGE ACTIN-BINDING PROTEIN MOLECULES IN SOLUTION AND INTERACTING WITH ACTIN-FILAMENTS
STRUCTURE OF MACROPHAGE ACTIN-BINDING PROTEIN MOLECULES IN SOLUTION AND INTERACTING WITH ACTIN-FILAMENTS
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DOI：
10.1016/0022-2836(81)90545-3
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发表时间：
1981-01-01
影响因子：
5.6
通讯作者：
STOSSEL, TP
中科院分区：
文献类型：
--
作者：
HARTWIG, JH;STOSSEL, TP
研究了[兔肺巨噬细胞]肌动蛋白结合蛋白分子在溶液中的结构及其与肌动蛋白丝的相互作用。在生理离子强度下，肌动蛋白结合蛋白的Mr[分子比]值为540倍。通过直接和间接的水动力测量确定。它是一种不对称的二聚体，由270。103个道尔顿亚基。在阴性染色或低角度阴影后的EM中，肌动蛋白结合蛋白分子具有广泛的构象，从封闭的圆形结构到轮廓长度为162 nm的完全延伸的链。显然，所有构型都源自同一结构，该结构由端到端连接的2个单体链组成。从EM图像确定的旋转半径为21.3 nm，与水动力分析计算的17.6 nm值一致。水动力测量的平均轴比为17:1，EM中完全伸展的二聚体分子的轴比为54:1。所有这些观察结果表明，肌动蛋白结合蛋白二聚体是非常灵活的。灵活性参数。lambda。（Landau and Lifshits, 1958），肌动蛋白结合蛋白的分子量为0.18 nm-1。通过沉降测定，肌动蛋白结合蛋白与肌动蛋白丝结合的Ka值为2倍。106 M-1和1二聚体到14个肌动蛋白单体的能力。经过高浓度（与肌动蛋白的摩尔比）的孵育。1:10)肌动蛋白结合蛋白与肌动蛋白丝的结合，在EM下可以看到长丝束。在这些条件下，肌动蛋白结合蛋白分子以规则的40 nm间隔或每15个单体装饰一次肌动蛋白束中的肌动蛋白丝，大约相当于通过沉淀测量的结合能力。低浓度的肌动蛋白结合蛋白（与肌动蛋白的摩尔比）。1:50)可以促进肌动蛋白丝在溶液中的凝胶化，但没有明显改变肌动蛋白丝的各向同性。肌动蛋白结合蛋白分子在肌动蛋白丝之间的EM直接可视化显示，二聚体足以交叉桥接肌动蛋白丝，肌动蛋白结合蛋白二聚体是双极性的，由头对头连接的单体组成，肌动蛋白结合位点位于自由尾部。肌动蛋白结合蛋白是生理离子强度的二聚体。每个二聚体有2个肌动蛋白丝结合位点，因此足以使肌动蛋白丝在溶液中凝胶化。肌动蛋白结合蛋白亚基的长度和灵活性使得这种分子在结构上适合于将大的螺旋细丝交联成各向同性网络。
The structure of [rabbit lung macrophage] actin-binding protein molecules in solution and interacting with actin filaments was examined. At physiological ionic strength, actin-binding protein has a Mr [molecular ratio] value of 540 .times. 103 as determined by direct and indirect hydrodynamic measurements. It is an asymmetrical dimer composed of 270 .times. 103 dalton subunits. Viewed in the EM after negative staining or low angle shadowing, actin-binding protein molecules assume a broad range of conformations varying from closed circular structures to fully extended strands 162 nm in contour length. All configurations are apparently derived from the same structure which consists of 2 monomer chains connected end-to-end. The radius of gyration determined from the EM images was 21.3 nm in agreement with the value of 17.6 nm calculated from hydrodynamic assays. The average axial ratio from hydrodynamic measurements was 17:1, fully extended dimer molecules in the EM would have an axial ratio of 54:1. All of these observations indicate that actin-binding protein dimers are extremely flexible. The flexibility parameter .lambda. (Landau and Lifshits, 1958) for actin-binding protein is 0.18 nm-1. As determined by sedimentation, actin-binding protein binds to actin filaments with a Ka value of 2 .times. 106 M-1 and a capacity of 1 dimer to 14 actin monomers in filaments. After incubation of high concentrations (molar ratio to actin .gtoreq. 1:10) of actin-binding protein with actin filaments, long filament bundles are visible by EM. Under these conditions, actin-binding protein molecules decorate the actin filaments in the bundles at regular 40 nm intervals or once every 15 monomers, approximately equivalent to the binding capacity measured by sedimentation. Low concentrations of actin-binding protein (molar ratio to actin .gtoreq. 1:50) which promote the gelation of actin filaments in solution, did not detectably alter the isotropy of the actin filaments. Direct visualization of actin-binding protein molecules between actin filaments by EM showed that dimers are sufficient for crossbridging of actin filaments and that actin-binding protein dimers are bipolar, composed of monomers connected head-to-head and having actin-binding sites located on the free tails. Actin-binding protein is a dimer at physiological ionic strength. Each dimer has 2 actin filament binding sites and is therefore sufficient to gel actin filaments in solution. The length and flexibility of the actin binding protein subunits render this molecule structurally suited for the crosslinking of large helical filaments into isotropic networks.