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Getting In or Out: Early Segregation Between Importers and Exporters in the Evolution of ATP-Binding Cassette (ABC) Transporters 总被引:17,自引:0,他引:17
ATP-binding cassette (ABC) systems, also called traffic ATPases, are found in eukaryotes and prokaryotes and almost all participate
in the transport of a wide variety of molecules. ABC systems are characterized by a highly conserved ATPase module called
here the ABC module, involved in coupling transport to ATP hydrolysis. We have used the sequence of one of the first representatives
of bacterial ABC transporters, the MalK protein, to collect 250 closely related sequences from a nonredundant protein sequence
database. The sequences collected by this objective method are all known or putative ABC transporters. After having eliminated
short protein sequences and duplicates, the 197 remaining sequences were subjected to a phylogenetic analysis based on a mutational
similarity matrix. An unrooted tree for these modules was found to display two major branches, one grouping all collected
uptake systems and the other all collected export systems. This remarkable disposition strongly suggests that the divergence
between these two functionally different types of ABC systems occurred once in the history of these systems and probably before
the differentiation of prokaryotes and eukaryotes. We discuss the implications of this finding and we propose a model accounting
for the generation and the diversification of ABC systems.
Received: 23 February 1997 / Accepted: 7 April 1998 相似文献