ROLE OF PHOSPHORYLATION AS A REGULATORY MECHANISM IN MUSCLE CONTRACTION

激酶相关蛋白（KRP），也称为telokin，是一种独立的 表达为“基因中的基因”。 它代表羧基末端 20，000 Da肌球蛋白轻链激酶（MLCK）。 其表达 由其启动子控制，该启动子位于MLCK基因的内含子内。 KRP不含酶或钙调蛋白结合位点， MLCK及其功能仍不清楚。 我们发现它能结合 平滑肌和非肌肉肌球蛋白，并可能在稳定 肌球蛋白丝。 非磷酸化脊椎动物平滑肌和 非肌肉肌球蛋白丝在生理离子强度， 通过在体外加入ATP解聚。 溶解的肌球蛋白 采用具有沉降系数的“折叠”单体构象， 的10 S。 KRP通过与肌球蛋白结合来防止这种解聚， 可能在“颈部”区域附近，即，头部和头部的连接处 亚片段2（S-2）区。 结合的化学计量似乎 为每摩尔肌球蛋白1摩尔KRP。 KRP与去磷酸化的平滑肌结合 和非肌肉肌球蛋白，但不磷酸化肌球蛋白或骨骼肌 肌球蛋白 KRP似乎不激活细胞的酶活性， 去磷酸化肌球蛋白，通过其对肌动蛋白活化的 MgATPase也不引起去磷酸化肌球蛋白移动肌动蛋白丝 在体外运动性测定中。 KRP确实与MLCK竞争 结合肌球蛋白肌动蛋白，但不完全抑制 MLCK对肌球蛋白的磷酸化。 在平滑肌组织中，每个肌球蛋白分子几乎有1个KRP。 我们 我认为KRP的功能可能是稳定肌球蛋白丝， 与肌球蛋白颈部的同一区域结合， 肌球蛋白结合形成10 S构象。 这将 解释了松弛的平滑肌组织含有 肌球蛋白粗丝，即使有一个非常低的水平， 轻链的磷酸化。

Kinase related protein (KRP), also called telokin, is an independently expressed "gene within a gene". It represents the carboxyl-terminal 20,000 Da of myosin light chain kinase (MLCK). Its expression is controlled by its promoter which lies within an intron of the MLCK gene. KRP does not contain the enzymatic nor the calmodulin-binding site of MLCK and its function has remained unknown. We have found that it binds to smooth muscle and nonmuscle myosin and may play a role in stabilizing myosin filaments. Unphosphorylated vertebrate smooth muscle and nonmuscle myosin filaments at physiological ionic strengths are depolymerized by the addition of ATP in vitro. The solubilized myosin adopts a "folded" monomeric conformation with a sedimentation coefficient of 10S. KRP prevents this depolymerization by binding to myosin, probably near the "neck" region, i.e., the junction of the head and the subfragment-two (S-2) region. The stoichiometry of binding appears to be 1 mol of KRP per mol of myosin. KRP binds to dephosphorylated smooth and nonmuscle myosin, but not to phosphorylated myosin or skeletal muscle myosin. KRP does not appear to activate the enzymatic activity of the dephosphorylated myosin as measured by its effects on the actin-activated MgATPase nor cause the dephosphorylated myosin to move actin filaments in an in vitro motility assay. KRP does compete with MLCK for the binding of myosin to actin, but does not fully inhibit the phosphorylation of myosin by MLCK. There is nearly 1 KRP per myosin molecule in smooth muscle tissue. We propose that KRP functions to stabilize myosin filaments possibly by binding to the same region in the neck region of myosin to which the tail of muscle myosin binds in forming the 10S conformation. This would account for the observation that relaxed smooth muscle tissue contains myosin thick filaments even though there is a very low level of phosphorylation of the light chains.