Littlefield R, Fowler V M
Department of Cell Biology, Scripps Research Institute, La Jolla, California 92037, USA.
Annu Rev Cell Dev Biol. 1998;14:487-525. doi: 10.1146/annurev.cellbio.14.1.487.
Actin filaments (thin filaments) are polymerized to strikingly uniform lengths in striated muscle sarcomeres. Yet, actin monomers can exchange dynamically into thin filaments in vivo, indicating that actin monomer association and dissociation at filament ends must be highly regulated to maintain the uniformity of filament lengths. We propose several hypothetical mechanisms that could generate uniform actin filament length distributions and discuss their application to the determination of thin filament length in vivo. At the Z line, titin may determine the minimum extent and tropomyosin the maximum extent of thin filament overlap by regulating alpha-actinin binding to actin, while a unique Z filament may bind to capZ and regulate barbed end capping. For the free portion of the thin filament, we evaluate possibilities that thin filament components (e.g. nebulin or the tropomyosin/troponin polymer) determine thin filament lengths by binding directly to tropomodulin and regulating pointed end capping, or alternatively, that myosin thick filaments, together with titin, determine filament length by indirectly regulating tropomodulin's capping activity.
在横纹肌肌节中，肌动蛋白丝（细肌丝）聚合成长度惊人一致的细丝。然而，肌动蛋白单体在体内可动态交换进入细肌丝，这表明肌动蛋白单体在细丝末端的结合和解离必须受到高度调控，以维持细丝长度的一致性。我们提出了几种可能产生均匀肌动蛋白丝长度分布的假设机制，并讨论了它们在体内细肌丝长度测定中的应用。在Z线处，肌联蛋白可能通过调节α - 辅肌动蛋白与肌动蛋白的结合来确定细肌丝重叠的最小范围，而原肌球蛋白则确定最大范围，同时一种独特的Z细丝可能与帽蛋白Z结合并调节肌动蛋白丝的带刺末端封端。对于细肌丝的自由部分，我们评估了以下可能性：细肌丝成分（如伴肌动蛋白或原肌球蛋白/肌钙蛋白聚合物）通过直接与原肌球蛋白调节蛋白结合并调节肌动蛋白丝的钝端封端来确定细肌丝长度，或者，肌球蛋白粗肌丝与肌联蛋白一起通过间接调节原肌球蛋白调节蛋白的封端活性来确定细丝长度。
