Lees-Miller S P, Anderson C W
Biology Department, Brookhaven National Laboratory, Upton, New York 11973.
J Biol Chem. 1989 Feb 15;264(5):2431-7.
Amino-terminal protein sequence analysis revealed that exponentially growing human HeLa cells at 37 degrees C express two closely related 90-kDa "heat shock" proteins (hsp 90) in nearly equal amounts. Both hsp 90s begin with proline; the initial methionine residue is removed. The alpha protein contains a 9-amino acid segment, TQTQDQPME, from residues 4 to 12, that is replaced by a 4-amino acid segment, VHHG, in the beta form. The purified hsp 90 mixture contains 2 mol of phosphate/mol of polypeptide. Both hsp 90 proteins are phosphorylated at two homologous sites. For the alpha protein, these sites correspond to serine 231 and serine 263. A 5-amino acid segment, ESEDK, between the two phosphorylation sites is absent from the beta protein. The sequence between phosphorylation sites of both hsp 90s is predicted to have alpha helical structure. Dephosphorylated hsp 90 is phosphorylated at both sites by casein kinase II from HeLa cells, calf thymus, or rabbit reticulocytes; no other hsp 90 residues were phosphorylated by casein kinase II in vitro.
氨基末端蛋白质序列分析显示，在37摄氏度下指数生长的人HeLa细胞以几乎相等的量表达两种密切相关的90 kDa“热休克”蛋白（hsp 90）。两种hsp 90均以脯氨酸开头；起始甲硫氨酸残基被去除。α蛋白在第4至12位残基处含有一个9个氨基酸的片段TQTQDQPME，在β形式中被一个4个氨基酸的片段VHHG取代。纯化的hsp 90混合物每摩尔多肽含有2摩尔磷酸盐。两种hsp 90蛋白在两个同源位点被磷酸化。对于α蛋白，这些位点对应于丝氨酸231和丝氨酸263。β蛋白在两个磷酸化位点之间不存在一个5个氨基酸的片段ESEDK。两种hsp 90磷酸化位点之间的序列预计具有α螺旋结构。去磷酸化的hsp 90在两个位点都被来自HeLa细胞、小牛胸腺或兔网织红细胞的酪蛋白激酶II磷酸化；在体外，酪蛋白激酶II未使其他hsp 90残基磷酸化。
