pKRP (kinase-related protein), also known as telokin, has been proposed to inhibit smooth muscle contractility by inhibiting the phosphorylation of the rMLC (regulatory myosin light chain) by the Casup2+/sup-activated MLCK (myosin light chain kinase). Using the phosphatase inhibitor microcystin, we show in the present study that KRP also inhibits Casup2+/sup-independent rMLC phosphorylation and smooth muscle contraction mediated by novel Casup2+/sup-independent rMLC kinases. Incubating KRP-depleted Triton-skinned taenia coli with microcystin at ip/iCa&8 induced a slow contraction reaching 90% of maximal force (iF/isubmax/sub) at ip/iCa 4.5 after ~25 min. Loading the fibres with KRP significantly slowed down the force development, i.e. the time to reach 50% of iF/isubmax/sub was increased from 8 min to 35 min. KRP similarly inhibited rMLC phosphorylation of HMM (heavy meromyosin) iin vitro/i by MLCK or by the constitutively active MLCK fragment (61K-MLCK) lacking the myosin-docking KRP domain. A C-terminally truncated KRP defective in myosin binding inhibited neither force nor HMM phosphorylation. Phosphorylated KRP inhibited the rMLC phosphorylation of HMM iin vitro/i and Casup2+/sup-insensitive contractions in fibres similar to unphosphorylated KRP, whereby the phosphorylation state of KRP was not altered in the fibres. We conclude that (i) KRP inhibits not only MLCK-induced contractions, but also those elicited by Casup2+/sup-independent rMLC kinases; (ii) phosphorylation of KRP does not modulate this effect; (iii) binding of KRP to myosin is essential for this inhibition; and (iv) KRP inhibition of rMLC phosphorylation is most probably due to the shielding of the phosphorylation site on the rMLC./p
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机译：有人提出>激酶相关蛋白（KRP），也称为telokin，它通过抑制Ca 2 + -使rMLC（调节性肌球蛋白轻链）磷酸化来抑制平滑肌收缩。激活的MLCK（肌球蛋白轻链激酶）。使用磷酸酶抑制剂微囊藻毒素，我们在本研究中表明，KRP还抑制由独立于Ca 2 + 的新型rMLC介导的不依赖Ca 2 + 的rMLC磷酸化和平滑肌收缩激酶。在 p Ca> 8处将KRP耗尽的Triton皮肤的牛带菌与微囊藻毒素一起孵育，引起缓慢收缩，达到最大力的90％（ F max ）在约25分钟后在 p Ca 4.5处。用KRP加载纤维会显着减慢力的发展，即达到 F max 的50％的时间从8分钟增加到35分钟。 KRP类似地通过MLCK或缺乏肌球蛋白对接KRP结构域的组成型活性MLCK片段（61K-MLCK）抑制HMM（重肌球蛋白）的rMLC磷酸化。 C端截短的肌球蛋白结合缺陷KRP既不抑制力也不抑制HMM磷酸化。与未磷酸化的KRP相似，磷酸化的KRP在体外抑制HMM 的rMLC磷酸化和Ca 2 + 不敏感的收缩，从而使纤维中KRP的磷酸化状态不变。我们得出以下结论：（i）KRP不仅抑制MLCK诱导的收缩，而且抑制不依赖Ca 2 + 的rMLC激酶引起的收缩; （ii）KRP的磷酸化不能调节这种作用; （iii）KRP与肌球蛋白的结合对于这种抑制是必不可少的; （iv）KRP抑制rMLC磷酸化的原因很可能是由于rMLC磷酸化位点的屏蔽。
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