Studies on structure and urea-resistibility of myosin from marine elasmobranchs.

目的：研究海丝兰中尿素含量在0.3 ~ 0.6 M范围内，对高渗透压海水产生抵抗作用。然而，即使在尿素存在的情况下，含尿素板鳃中的蛋白质也能像硬骨鱼的蛋白质一样在没有尿素的情况下保持其生理功能。本研究的目的是分析安魂鲨肌球蛋白尿素耐受性的机制。我们检测了肌动蛋白激活的Mg^<2+> - atp酶活性，以探讨肌动蛋白在鲨鱼肌球蛋白产生尿素抗性中的可能作用。据推测，肌动蛋白与肌凝蛋白的相互作用可能稳定了鲨鱼肌凝蛋白的结构。（Kanoh et, 1999）2安魂鲨肌球蛋白、棒和S1制剂的α-螺旋含量随着尿素浓度的增加而降低。而棒材对尿素处理最稳定。此外，当尿素从样品溶液中去除时，α-螺旋结构完全折叠，表明其具有较高的尿素抗性。（Kanoh et al., 2000）3鲨鱼肌球蛋白的表面疏水性比鲤鱼肌球蛋白对尿素处理的抗性更强，S1和rod的连接区域是造成安魂鱼和鲤鱼肌球蛋白差异的主要原因。（Kanoh et al., 2000）4补偿高浓度尿素不良影响的调节机制与形成对尿素具有抗性的蛋白质结构有关，至少在海洋板鳃草的肌纤维atp酶的情况下是这样。（Kanoh et al, 2001）5从cDNA核苷酸序列推断出肌球蛋白重链和A1、A2和DTNB轻链三种类型的氨基酸序列，分别预测1937、193、150和168个氨基酸残基。重链氨基酸序列与恒温动物的同源性较高（85%），分别为686 ~ 693、788 ~ 794、885 ~ 895和983 ~ 988。（Kanoh et al., 2002）

ObjectiveElasmobranch contain urea, in the range of 0.3 to 0.6 M to exert resistancy against high osmolarity of seawater. However, proteins in urea-containing elasmobranch can maintain their physiological functions even in the presence of urea as proteins of teleost in the absence of urea. The objective of this study was to analyze the mechanism underlying urea-resistibility of requiem shark myosin.Project1 We examined the actin-activated Mg^<2+> - ATPase activity to probe a possible role of actin in producing urea-resistibility for shark myosin. It was assumed that the interaction between actin and myosin may stabilize the structure of shark myosin. (Kanoh et al, 1999)2 Myosin, rod and S1 preparations from requiem shark showed decreased α-helical contents with increasing urea concentrations. However, rod was most stable against urea treatment. Furthermore, α-helical structure were completely refolded when urea was removed from the sample solutions, demonstrating their high urea-resistibility.(Kanoh et al., 2000)3 Surface hydrophobicity of shark myosin is more resistant to urea treatments than carp myosin, and that the region connecting S1 and rod is most responsible for such differences between requiem shark and carp myosins. (Kanoh et al., 2000)4 The regulatory mechanisms to compensate for the undesirable effects of urea at high concentrations are related to developing protein structures that are resistant to urea, at least in the case of myofibrillar ATPase in marine elasmobranch. (Kanoh et al, 2001)5 The amino acid sequence of myosin heavy chain and three types of A1, A2 and DTNB light chains were deduced from cDNA nucleotide sequences, predicting 1937, 193, 150 and 168 amino acid residues respectively. The amino acid sequence of heavy chain showed high identity(85 %) with those from homeotherm rather than from fishes and was characteristic at 686-693, 788-794, 885-895 and 983-988. (Kanoh et al., 2002)