Two tandemly linked identical genes code for the glycosomal glyceraldehyde‐phosphate dehydrogenase in Trypanosoma brucei.
Two tandemly linked identical genes code for the glycosomal glyceraldehyde‐phosphate dehydrogenase in Trypanosoma brucei.
复制标题
两个串联连接的基因与布氏锥虫中糖体甘油醛磷酸脱氢酶的编码相同。
作者：
P. Michels;A. Poliszczak;Klaas A. Osingal;O. Misset;J. V. Beeumen;R. Wierenga;Piet;'. Borst;F. Opperdoes
布氏锥虫含有两种甘油醛-磷酸脱氢酶同工酶，一种存在于微体状细胞器中，即糖体中，另一种存在于胞浆中。我们在这里表明，糖体酶是由两个相同序列的连锁基因编码的。这些基因编码一种由358个氨基酸组成的蛋白质，其摩尔分数为1。WT为38.9kd。这比到目前为止研究的所有其他GAPDH蛋白都要大得多，包括位于锥虫胞浆中的酶。该糖体酶与其他10种生物(原核生物和真核生物)的已知GAPDH蛋白序列显示52-57%的同源性。参与NAD+结合、催化和亚基接触的残基在所有这些GAPDH分子之间都是保守的，包括锥体分子。然而，布氏毛滴虫的糖体蛋白具有一些明显的特征。首先，它含有许多插入片段，长度为1-8个氨基酸，这是导致高摩尔数的原因。蛋白质的WT。其次，异常多的带正电的氨基酸赋予了蛋白质很高的等电点(等电点9.3)。部分额外的碱性残基存在于插入物中。我们讨论了糖体GAPDH基因的基因组组织，以及蛋白质的特殊特性参与了它从细胞质转移到糖体的可能性。
Trypanosoma brucei contains two isoenzymes for glyceraldehyde‐phosphate dehydrogenase (GAPDH); one enzyme resides in a microbody‐like organelle, the glycosome, the other one is found in the cytosol. We show here that the glycosomal enzyme is encoded by two tandemly linked genes of identical sequence. These genes code for a protein of 358 amino acids, with a mol. wt of 38.9 kd. This is considerably larger than all other GAPDH proteins studied so far, including the enzyme that is located in the cytosol of the trypanosome. The glycosomal enzyme shows 52‐57% homology with known sequences of GAPDH proteins from 10 other organisms, both prokaryotes and eukaryotes. The residues that are involved in NAD+ binding, catalysis and subunit contacts are well conserved between all these GAPDH molecules, including the trypanosomal one. However, the glycosomal protein of T. brucei has some distinct features. Firstly, it contains a number of insertions, 1‐8 amino acids long, which are responsible for the high mol. wt of the protein. Secondly, an unusually high number of positively charged amino acids confer a high isoelectric point (pI 9.3) to the protein. Part of the additional basic residues are present in the insertions. We discuss the genomic organization of the genes for the glycosomal GAPDH and the possibility that the particular features of the protein are involved in its transfer from the cytoplasm, where it is synthesized, into the glycosome.