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首页> 外文期刊>Molecular and Cellular Biology >Sequence Requirements for Trafficking of the CRAM Transmembrane Protein to the Flagellar Pocket of African Trypanosomes
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Sequence Requirements for Trafficking of the CRAM Transmembrane Protein to the Flagellar Pocket of African Trypanosomes

机译：CRAM跨膜蛋白向非洲锥虫的鞭毛袋运输的序列要求。

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CRAM is a cysteine-rich acidic transmembrane protein, highly expressed in the procyclic form of Trypanosoma brucei. Cell surface expression of CRAM is restricted to the flagellar pocket of trypanosomes, the only place where receptor mediated endocytosis takes place in the parasite. CRAM can function as a receptor and was hypothesized to be a lipoprotein receptor of trypanosomes. We study mechanisms involved in the presentation and routing of CRAM to the flagellar pocket of insect- and bloodstream-form trypanosomes. By deletional mutagenesis, we found that deleting up to four amino acids from the C terminus of CRAM did not affect the localization of CRAM at the flagellar pocket. Shortening the CRAM protein by 8 and 19 amino acids from the C terminus resulted in the distribution of the CRAM protein in the endoplasmic reticulum (ER) (the CRAM protein is no longer uniquely sequestered at the flagellar pocket). This result indicates that the truncation of the CRAM C terminus affected the transport efficiency of CRAM from the ER to the flagellar pocket. However, when CRAM was truncated between 29 and 40 amino acids from the C terminus, CRAM was not only distributed in the ER but also located to the flagellar pocket and spread to the cell surface and the flagellum. Replacing the CRAM transmembrane domain with the invariant surface glycoprotein 65-derived transmembrane region did not affect the flagellar pocket location of CRAM. These results indicate that the CRAM cytoplasmic extension may exhibit two functional domains: one domain near the C terminus is important for efficient export of CRAM from the ER, while the second domain is of importance for confining CRAM to the flagellar pocket membrane.
机译：CRAM是富含半胱氨酸的酸性跨膜蛋白，以布鲁姆锥虫（Trypanosoma brucei）的前环形式高表达。 CRAM的细胞表面表达仅限于锥虫的鞭毛袋，锥虫是受体介导的内吞作用发生的唯一场所。 CRAM可以充当受体，并被认为是锥虫的脂蛋白受体。我们研究的机制涉及到昆虫和血液形式锥虫的鞭毛袋的CRAM的提出和路由。通过删除突变，我们发现从CRAM的C末端删除最多四个氨基酸不会影响CRAM在鞭毛袋中的定位。将CRAM蛋白从C末端缩短8个和19个氨基酸，导致CRAM蛋白在内质网（ER）中分布（CRAM蛋白不再唯一地隔离在鞭毛袋中）。该结果表明CRAM C末端的截短影响了CRAM从ER到鞭毛袋的转运效率。但是，当CRAM从C末端被截短29至40个氨基酸时，CRAM不仅分布在ER中，而且位于鞭毛袋中并扩散到细胞表面和鞭毛。用不变的表面糖蛋白65衍生的跨膜区替换CRAM跨膜结构域不会影响CRAM的鞭毛袋位置。这些结果表明，CRAM胞质延伸区可能显示两个功能域：靠近C末端的一个域对于从ER有效输出CRAM很重要，而第二个域对于将CRAM限制在鞭毛袋膜上很重要。

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