Thøgersen Ida B, Hammes Stephen R, Rubenstein David S, Pizzo Salvatore V, Valnickova Zuzana, Enghild Jan J
Department of Molecular and Structural Biology, University of Arhus, Gustav Wieds Vej 10C, Aarhus, Denmark.
Biochim Biophys Acta. 2002 Jul 29;1598(1-2):131-9. doi: 10.1016/s0167-4838(02)00360-6.
The amino acid sequence of the monomeric alpha-macroglobulin (alphaM) from the American bullfrog, Rana catesbiana, was determined. The mature protein consisted of 1469 amino acid residues and shared sequence identity with other members of the alphaM family of protein. The central portion of the frog monomeric alphaM contained Cys residues positioned analogously to the Cys residues in human alpha(2)-macroglobulin (alpha(2)M), known to be involved in disulfide bridges. Additionally, the frog monomeric alphaM contained six Cys residues in a approximately 60 residue COOH-terminal extension not present in previously characterized alphaMs. The spacing of the Cys residues and the overall sequence identity of this COOH-terminal extension were consistent with a trefoil motif. This is the first time a member of the trefoil factor family has been identified in the circulatory system. The "bait region" was located between Arg(675)-Lys(685) and contained mainly basic amino acid residues. The COOH-terminal receptor-binding domain was not exposed prior to proteolysis of this highly susceptible region. The proximity of the receptor-binding and trefoil domains implied that the trefoil domain is similarly concealed before bait region cleavage.
测定了美国牛蛙（Rana catesbiana）单体α-巨球蛋白（αM）的氨基酸序列。成熟蛋白由1469个氨基酸残基组成，与αM蛋白家族的其他成员具有序列同源性。青蛙单体αM的中央部分含有与人类α2-巨球蛋白（α2M）中已知参与二硫键形成的半胱氨酸残基位置类似的半胱氨酸残基。此外，青蛙单体αM在先前已鉴定的αM中不存在的约60个残基的COOH末端延伸中含有六个半胱氨酸残基。半胱氨酸残基的间距以及该COOH末端延伸的整体序列同源性与三叶基序一致。这是首次在循环系统中鉴定出三叶因子家族的成员。“诱饵区域”位于Arg(675)-Lys(685)之间，主要包含碱性氨基酸残基。在这个高度敏感区域进行蛋白水解之前，COOH末端受体结合结构域并未暴露。受体结合结构域和三叶结构域的接近表明，在诱饵区域切割之前，三叶结构域同样是被隐藏的。
