Kueng V, Schlaeppi K, Schneider A, Seebeck T
Institut für allgemeine Mikrobiologie, Universität Bern, Switzerland.
J Biol Chem. 1989 Mar 25;264(9):5203-9.
Glycosomes are specialized organelles of trypanosomes which contain glycolytic enzymes as their major protein components in Trypanosoma brucei bloodstream form. In the glycosomes of the insect form of T. brucei, additional enzyme activities are found but have not yet been ascribed to a particular protein molecule. In this study, we report the characterization of a 60-kDa glycosomal protein (p60) encoded by a single copy gene which is transcribed into a mRNA of 2.9 kilobases. The gene codes for a protein of 472 amino acids with a molecular mass of 52.5 kDa, suggesting that the mRNA contains large untranslated regions of about 1.4 kilobases. Genomic DNA hybridizations have shown that the gene for p60 is confined to the family of Trypanosomatidae. Sequence comparison confirmed that p60 is not a member of a conserved protein family and does not belong to the group of glycolytic enzymes. p60 is expressed much more strongly in insect form than in bloodstream form trypanosomes. Thus, p60 is the first glycosomal protein observed whose expression is up-regulated during the transition of trypanosomes from the bloodstream to the insect form. The biochemical characterization of p60 demonstrated its capability to bind microtubules and membrane vesicles and to cross-link these structures. These properties might indicate a function in linking glycosomes to the microtubules of the trypanosomal cytoskeleton. However, proteinase K digestion experiments indicate that p60 is not exposed at the outer surface of the glycosomal membrane. The biological role of the microtubule-binding capability of p60 remains unclear, whereas its membrane binding may be of physiological significance inside the glycosome.
糖体是锥虫的特殊细胞器，在布氏锥虫血流型中，其主要蛋白质成分包含糖酵解酶。在布氏锥虫昆虫型的糖体中，发现了其他酶活性，但尚未归因于特定的蛋白质分子。在本研究中，我们报告了一种由单拷贝基因编码的60 kDa糖体蛋白（p60）的特性，该基因转录成2.9千碱基的mRNA。该基因编码一个由472个氨基酸组成、分子量为52.5 kDa的蛋白质，这表明该mRNA含有约1.4千碱基的大非翻译区。基因组DNA杂交表明，p60基因仅限于锥虫科。序列比较证实，p60不是保守蛋白家族的成员，也不属于糖酵解酶组。p60在昆虫型中的表达比在血流型锥虫中强烈得多。因此，p60是观察到的第一个在锥虫从血流型向昆虫型转变过程中表达上调的糖体蛋白。p60的生化特性表明它能够结合微管和膜泡，并使这些结构交联。这些特性可能表明其在将糖体与锥虫细胞骨架的微管连接方面具有功能。然而，蛋白酶K消化实验表明，p60未暴露在糖体膜的外表面。p60与微管结合能力的生物学作用尚不清楚，而其与膜的结合在糖体内可能具有生理意义。
