Elucidation of the molecular mechanism of urea-resistibility, comparing the structural difference between freshwater ray and marine shark myosin

除了一些淡水鳐外，海洋鲨鱼含有0.2至0.6 M范围内的尿素，这是最典型的蛋白质变性剂之一，以抵抗高渗透压海水。然而，含尿素的鲨鱼中的蛋白质即使在尿素存在下也可以保持其生理功能，就像硬骨鱼在没有尿素的情况下的蛋白质一样。来自海洋鲨鱼的蛋白质被认为是通过一些分子机制保护不变性的。本研究旨在通过对淡水鳐肌球蛋白一级结构的分析和安魂鲨肌球蛋白一级结构的比较，验证上述关于鲨鱼肌球蛋白尿素吸收性的分子机制的假设。在0.3M尿素浓度下达到最大值，然后随着尿素浓度的增加而逐渐下降。另一方面，鲤鱼的活性被添加 ...更多信息 尿素，即使在低浓度和迅速下降，随着尿素浓度的增加。淡水射线的活动接近于安魂鱼和鲤鱼相对活动的平均值。结果表明，淡水鳐肌球蛋白是研究其尿素溶解性的理想材料。根据淡水鳐肌球蛋白的cDNA核苷酸序列，推导了淡水鳐肌球蛋白的氨基酸序列，预测了1933个氨基酸。本研究将淡水鳐肌球蛋白的1788个氨基酸残基与安魂鲨和其他硬骨鱼的肌球蛋白进行了比较。785-793位残基位于肌球蛋白重链S1区的必需轻链结合位点。与其他硬骨鱼相比，安魂鲨和淡水鳐肌球蛋白的氨基酸序列显示出极端的亲水性，但797-799位残基显示出疏水性。第685-693位残基位于S1区ATP和肌动蛋白结合位点附近。淡水鳐肌球蛋白的这一序列显示了鲤鱼和鲨鱼之间的亲水性。这一区域与ATP酶活性结构域接近，并与尿素溶解性有关。所得结果阐明了海鲨尿素吸收的部分分子机理。少

Marine sharks except for some freshwater rays contain urea, one of the most typical protein denaturants, in the range of 0.2 to 0.6 M to exert resistancy against high osmolarity of seawater. However, proteins in urea-containing sharks can maintain their physiological functions even in the presence of urea as proteins of teleost in the absence of urea. The proteins from marine sharks are supposed to be protected from denaturation by some molecular mechanisms. The objective of this study was to analyze the primary structure of freshwater ray myosin and to compare those of requiem shark to test the above assumption on the molecular mechanism underlying urea-resistibility of marine shark myosin.The myofibrillar Mg^<2+>-ATPase activity of requiem shark was gradually decreased with increasing urea concentrations, showing maximal value at around 0.3 M urea and then declined gradually with increasing urea concentrations. On the other hand, the activity of carp was decreased by the addition of … More urea even at a low concentration and declined rapidly with increasing urea concentrations. The activity of freshwater ray was nearly the average of the relative activities of requiem shark and carp. These results indicated that the myosin from freshwater ray is suitable material for the research of the urea-resistibility.The amino acid sequence of skeletal muscle myosin from freshwater ray was deduced from cDNA nucleotide sequence, predicting 1933 amino acid residues. In this study,1788 amino acid residues from freshwater ray myosin were compared with those of requiem shark and other teleost. The residues 785-793 located in essential light chain binding site in the myosin heavy chain S1 region. This amino acid sequence of requiem shark and freshwater ray myosin showed extreme hydrohilicity comparing with those of other teleost, but the residues 797-799 showed hydrophobicity. The residues 685-693 located around the ATP and actin-binding site in S1 region. This sequence of freshwater ray myosin showed the hydropathy between carp and shark. This region is close to the ATPase activity domain, and the relevance to the urea-resistibility was indicated. The obtained results elucidate a part of molecular mechanism of urea-resistibility of the marine shark. Less