Comparative Analyses of Fundamental Differences in Membrane Transport Capabilities in Prokaryotes and Eukaryotes

Whole-genome transporter analyses have been conducted on 141 organisms whose complete genome sequences are available. For each organism, the complete set of membrane transport systems was identified with predicted functions, and classified into protein families based on the transporter classification system. Organisms with larger genome sizes generally possessed a relatively greater number of transport systems. In prokaryotes and unicellular eukaryotes, the significant factor in the increase in transporter content with genome size was a greater diversity of transporter types. In contrast, in multicellular eukaryotes, greater number of paralogs in specific transporter families was the more important factor in the increase in transporter content with genome size. Both eukaryotic and prokaryotic intracellular pathogens and endosymbionts exhibited markedly limited transport capabilities. Hierarchical clustering of phylogenetic profiles of transporter families, derived from the presence or absence of a certain transporter family, showed that clustering patterns of organisms were correlated to both their evolutionary history and their overall physiology and lifestyles.

本研究针对141个已获取完整基因组序列的生物开展了全基因组转运蛋白分析。针对每个生物，研究团队鉴定了其完整的膜转运系统集合并预测其功能，同时依据转运蛋白分类系统（transporter classification system）将其归类至不同蛋白质家族。基因组规模更大的生物，其转运系统的数量通常相对更多。在原核生物与单细胞真核生物中，伴随基因组规模扩大而使转运蛋白含量提升的关键因素，是转运蛋白类型的多样性更为丰富。与之相反，在多细胞真核生物中，特定转运蛋白家族旁系同源基因（paralogs）数量的增加，才是伴随基因组规模扩大提升转运蛋白含量的更主要因素。无论是真核还是原核的胞内病原体（intracellular pathogens）与内共生体（endosymbionts），其转运能力均显著受限。基于特定转运蛋白家族的有无所构建的转运蛋白家族系统发育谱（phylogenetic profiles），经层次聚类分析后发现：生物的聚类模式与其进化历史、整体生理特征及生活方式均存在相关性。