Structural and functional similarities between the nucleotide-binding domains of CFTR and GTP-binding proteins.
The opening and closing of the CFTR Cl- channel are regulated by ATP hydrolysis at its two nucleotide binding domains (NBDs). However, the mechanism and functional significance of ATP hydrolysis are unknown. Sequence similarity between the NBDs of CFTR and GTP-binding proteins suggested the NBDs might have a structure and perhaps a function like that of GTP-binding proteins. Based on this similarity, we predicted that the terminal residue of the LSGGQ motif in the NBDs of CFTR corresponds to a highly conserved glutamine residue in GTP-binding proteins that directly catalyzes the GTPase reaction. Mutations of this residue in NBD1 or NBD2, which were predicted to increase or decrease the rate of hydrolysis, altered the duration of channel closed and open times in a specific manner without altering ion conduction properties or ADP-dependent inhibition. These results suggest that the NBDs of CFTR, and consequently other ABC transporters, may have a structure and a function analogous to those of GTP-binding proteins. We conclude that the rates of ATP hydrolysis at NBD1 and at NBD2 determine the duration of the two states of the channel, closed and open, much as the rate of GTP hydrolysis by GTP-binding proteins determines the duration of their active state.
Carson
M R
MR
Howard Hughes Medical Institute, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242, USA.
Welsh
M J
MJ
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D006160:Guanosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007473:Ion Channels / Q000502:physiology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D018528:ATP-Binding Cassette Transporters; C505032:CFTR protein, human; D007473:Ion Channels; D011994:Recombinant Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D019204:GTP-Binding Proteins