title: The Max homodimeric b-HLH-LZ significantly interferes with the specific heterodimerization between the c-Myc and Max b-HLH-LZ in absence of DNA: a quantitative analysis.
abstract: Specific heterodimerization plays a crucial role in the regulation of the biology of the cell. For example, the specific heterodimerization between the b-HLH-LZ transcription factors c-Myc and Max is a prerequisite for c-Myc transcriptional activity that leads to cell growth, proliferation and tumorigenesis. On the other hand, the Mad proteins can compete with c-Myc for Max. The Mad/Max heterodimer antagonizes the effect of the c-Myc/Max heterodimer. In this contribution, we have focused on the specific heterodimerization between the b-HLH-LZ domains of c-Myc and Max using CD and NMR. While the c-Myc and Max b-HLH-LZ domains are found to preferentially form a heterodimer; we demonstrate for the first time that a significant population of the Max homodimeric b-HLH-LZ can also form and hence interferes significantly with the specific heterodimerization. This indicates that the Max/Max homodimer can also interfere with c-Myc/Max functions, therefore adding to the complexity of the regulation of transcription by the Myc/Max/Mad network. The demonstration of the existence of the homodimeric population was made possible by the application of numerical routines that enable the simulation of composite spectroscopic signal (e.g. CD) as a function of temperature and total concentration of proteins. From a systems biology perspective, our routines may be of general interest as they offer the opportunity to treat many competing equilibriums in order to predict the probability of existence of protein complexes.
authors.affiliation: Département de Pharmacologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: François-Olivier
authors.initials: FO
authors.lastname: McDuff
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Naud
authors.forename: Martin
authors.initials: M
authors.lastname: Montagne
authors.forename: Simon
authors.initials: S
authors.lastname: Sauvé
authors.forename: Pierre
authors.initials: P
authors.lastname: Lavigne
mesh_terms: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000378:metabolism*
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D016271:Proto-Oncogene Proteins c-myc; D004247:DNA