De Baere I, Derua R, Janssens V, Van Hoof C, Waelkens E, Merlevede W, Goris J
Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.
Biochemistry. 1999 Dec 14;38(50):16539-47. doi: 10.1021/bi991646a.
The carboxyl methyltransferase, which is claimed to exclusively methylate the carboxyl group of the C-terminal leucine residue of the catalytic subunit of protein phosphatase 2A (Leu(309)), was purified from porcine brain. On the basis of tryptic peptides, the cDNA encoding the human homologue was cloned. The cDNA of this gene encodes for a protein of 334 amino acids with a calculated M(r) of 38 305 and a predicted pI of 5.72. Database screening reveals the presence of this protein in diverse phyla. Sequence analysis shows that the novel methyltransferase is distinct from other known protein methyltransferases, sharing only sequence motifs supposedly involved in the binding of adenosylmethionine. The recombinant protein expressed in bacteria is soluble and the biophysical, catalytic, and immunological properties are indistinguishable from the native enzyme. The methylation of PP2A by the recombinant protein is restricted to Leu(309) of PP2A(C). No direct effects on phosphatase activity changes were observed upon methylation of the dimeric or trimeric forms of PP2A.
羧甲基转移酶据称专门对蛋白磷酸酶2A催化亚基的C末端亮氨酸残基（Leu(309)）的羧基进行甲基化，该酶是从猪脑中纯化得到的。基于胰蛋白酶肽段，克隆了编码人同源物的cDNA。该基因的cDNA编码一个334个氨基酸的蛋白质，计算所得的分子量为38305，预测的等电点为5.72。数据库筛选显示该蛋白存在于多种生物门类中。序列分析表明，这种新型甲基转移酶与其他已知的蛋白质甲基转移酶不同，仅共享推测参与腺苷甲硫氨酸结合的序列基序。在细菌中表达的重组蛋白是可溶的，其生物物理、催化和免疫学性质与天然酶无法区分。重组蛋白对PP2A的甲基化作用仅限于PP2A(C)的Leu(309)。PP2A的二聚体或三聚体形式甲基化后，未观察到对磷酸酶活性变化有直接影响。
