Mechanism of transcription factor recruitment by acidic activators.
Many transcriptional activators are intrinsically unstructured yet display unique, defined conformations when bound to target proteins. Target-induced folding provides a mechanism by which activators could form specific interactions with an array of structurally unrelated target proteins. Evidence for such a binding mechanism has been reported previously in the context of the interaction between the cancer-related c-Myc protein and the TATA-binding protein, which can be modeled as a two-step process in which a rapidly forming, low affinity complex slowly converts to a more stable form, consistent with a coupled binding and folding reaction. To test the generality of the target-induced folding model, we investigated the binding of two widely studied acidic activators, Gal4 and VP16, to a set of target proteins, including TATA-binding protein and the Swi1 and Snf5 subunits of the Swi/Snf chromatin remodeling complex. Using surface plasmon resonance, we show that these activator-target combinations also display bi-phasic kinetics suggesting two distinct steps. A fast initial binding phase that is inhibited by high ionic strength is followed by a slow phase that is favored by increased temperature. In all cases, overall affinity increases with temperature and, in most cases, with increased ionic strength. These results are consistent with a general mechanism for recruitment of transcriptional components to promoters by naturally occurring acidic activators, by which the initial contact is mediated predominantly through electrostatic interactions, whereas subsequent target-induced folding of the activator results in a stable complex.
Ferreira
Monica E
ME
Department of Life Sciences, Södertörns Högskola, S-141 89 Huddinge, Sweden. monica.ferreira@sh.se
Hermann
Stefan
S
Prochasson
Philippe
P
Workman
Jerry L
JL
Berndt
Kurt D
KD
Wright
Anthony P H
AP
D002843:Chromatin / Q000737:chemistry; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000378:metabolism; D017405:Herpes Simplex Virus Protein Vmw65 / Q000378:metabolism; D007477:Ions; D007700:Kinetics; D046911:Macromolecular Substances / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D020349:Surface Plasmon Resonance; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C052130:GAL4 protein, S cerevisiae; D017405:Herpes Simplex Virus Protein Vmw65; D007477:Ions; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; C066190:SNF5 protein, S cerevisiae; C078562:SWI1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D005982:Glutathione Transferase