The essential light chains constitute part of the active site of smooth muscle myosin.
The essential light chains constitute part of the active site of smooth muscle myosin.
复制标题
必需轻链构成平滑肌肌球蛋白活性位点的一部分。
作者：
Okamoto,Y;Sekine,T;Grammer,J;Yount,RG
肌球蛋白是一种主要的收缩蛋白，其特征是具有一个长的卷曲螺旋α-螺旋尾部和两个头部。每个头部包含肌动蛋白结合位点和ATP酶位点，并且由两条重链之一的NH 2末端的一半（相对分子质量，Mr，200，000）和一对轻链形成;所谓的调节轻链和必需轻链，每条约Mr 20，000。最近，我们已经确定了1 Trp 130的肌球蛋白重链从兔骨骼肌作为一个活性位点的氨基酸残基标记后，一个新的光亲和类似物的ADP，N-（4-叠氮基-2-硝基苯基）-2-氨乙基二磷酸（NANP）2。通过首先用硫醇交联剂3在活性位点捕获NANDP来消除非特异性标记。仅标记重链而不标记轻链与先前的发现4，5一致，即重链单独含有兔骨骼肌球蛋白的肌动蛋白激活的Mg-ATP酶活性。在这里，我们报告了类似的光标记实验与平滑肌肌球蛋白（鸡砂囊），其中3 H-NANDP被困在活性位点与钒6，这表明，重链和必需的轻链标记。结果表明，这两条链都有助于ATP结合位点，并代表了任何类型肌球蛋白活性位点中必需轻链参与的第一个直接证据。
Myosin, a major contractile protein, characteristically possesses a long coiled-coil α-helical tail and two heads. Each head contains both an actin binding site and an ATPase site and is formed from the NH2-terminal half of one of the two heavy chains (relative molecular mass, Mr, 200,000) and a pair of light chains; the so-called regulatory and essential light chains of approximately Mr20,000 each. Recently we have identified1Trp 130 of the myosin heavy chain from rabbit skeletal muscle as an active-site amino-acid residue after labelling with a new photoaffinity analogue of ADP,N-(4-azido-2-nitrophenyl)-2-aminoethyl diphosphate (NANDP)2. Nonspecific labelling was eliminated by first trapping NANDP at the active site with thiol crosslinking agents3. Exclusive labelling of the heavy chains with no labelling of the light chains agreed with previous findings4,5that the heavy chains alone contain the actin-activated Mg-ATPase activity of rabbit skeletal myosin. Here we report similar photolabelling experiments with smooth muscle myosin (chicken gizzard) in which3H-NANDP is trapped at the active site with vanadate6and which show that both the heavy chains and the essential light chains are labelled. The results indicate that both chains contribute to the ATP binding site and represent the first direct evidence for participation of the essential light chains in the active site of any type of myosin.