Evolutionary Analyses of ABC Transporters of Dictyostelium discoideum

The ABC superfamily of genes is one of the largest in the genomes of both bacteria and eukaryotes. The proteins encoded by these genes all carry a characteristic 200- to 250-amino-acid ATP-binding cassette that gives them their family name. In bacteria they are mostly involved in nutrient import, while in eukaryotes many are involved in export. Seven different families have been defined in eukaryotes based on sequence homology, domain topology, and function. While only 6 ABC genes in Dictyostelium discoideum have been studied in detail previously, sequences from the well-advanced Dictyostelium genome project have allowed us to recognize 68 members of this superfamily. They have been classified and compared to animal, plant, and fungal orthologs in order to gain some insight into the evolution of this superfamily. It appears that many of the genes inferred to have been present in the ancestor of the crown organisms duplicated extensively in some but not all phyla, while others were lost in one lineage or the other.

ABC基因超家族（ABC superfamily）是细菌与真核生物基因组中规模最大的基因家族之一。该家族编码的所有蛋白质均携带一段特征性的200至250个氨基酸的ATP结合盒（ATP-binding cassette），这也是该家族名称的由来。在细菌中，这类蛋白主要参与营养物质的跨膜输入；而在真核生物中，多数则负责物质的跨膜输出。基于序列同源性、结构域拓扑结构与功能，真核生物中的ABC超家族已被划分为7个不同的亚家族。此前仅有6个盘基网柄菌（Dictyostelium discoideum）的ABC基因得到了深入研究，但借助推进至较高阶段的盘基网柄菌基因组计划所产出的序列数据，我们共鉴定出该超家族的68个成员。我们对这些成员进行了分类，并与动物、植物及真菌的直系同源基因（orthologs）进行比对，以期深入解析该超家族的演化历程。研究结果显示，诸多被推断存在于冠群生物祖先体内的ABC基因，在部分而非全部演化类群中发生了大规模复制事件，而另有部分基因则在特定演化支系中发生了丢失。