Repressor binding to a dorsal regulatory site traps human eIF4E in a high cap-affinity state.
Eukaryotic translation initiation involves recognition of the 5' end of cellular mRNA by the cap-binding complex known as eukaryotic initiation factor 4F (eIF4F). Initiation is a key point of regulation in gene expression in response to mechanisms mediated by signal transduction pathways. We have investigated the molecular interactions underlying inhibition of human eIF4E function by regulatable repressors called 4E-binding proteins (4E-BPs). Two essential components of eIF4F are the cap-binding protein eIF4E, and eIF4G, a multi-functional protein that binds both eIF4E and other essential eIFs. We show that the 4E-BPs 1 and 2 block the interaction between eIF4G and eIF4E by competing for binding to a dorsal site on eIF4E. Remarkably, binding of the 4E-BPs at this dorsal site enhances cap-binding via the ventral cap-binding slot, thus trapping eIF4E in inactive complexes with high affinity for capped mRNA. The binding contacts and affinities for the interactions between 4E-BP1/2 and eIF4E are distinct (estimated K(d) values of 10(-8) and 3x10(-9) for 4E-BP1 and 2, respectively), and the differences in these properties are determined by three amino acids within an otherwise conserved motif. These data provide a quantitative framework for a new molecular model of translational regulation.
Ptushkina
M
M
Posttranscriptional Control Group, Department of Biomolecular Sciences, UMIST, PO Box 88, Manchester M60 1QD, UK.
von der Haar
T
T
Karim
M M
MM
Hughes
J M
JM
McCarthy
J E
JE
D048868:Adaptor Proteins, Signal Transducing; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D039642:Eukaryotic Initiation Factors; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010448:Peptide Initiation Factors / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D012313:RNA / Q000235:genetics / Q000378:metabolism; D012315:RNA Caps / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; C104151:EIF4EBP2 protein, human; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D039642:Eukaryotic Initiation Factors; D010448:Peptide Initiation Factors; D010750:Phosphoproteins; D012315:RNA Caps; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D012313:RNA