14-3-3 is a family of highly conserved and ubiquitously expressed eukaryotic proteins. 14-3-3 proteins have regulatory function and act in multiple cellular processes such as cell cycle, signal transduction or cell death. For the proper function of this rigid and highly helical protein, its dimeric state is essential [1]. Mammalian 14-3-3 proteins have 7 known isoforms named β, γ, ε, ξ, η, θ and σ, which can form both homo- and heterodimers. These isoforms differ in expression levels in various tissues, thus in their total concentrations in these tissues [2].
Most studies of 14-3-3 proteins to date have been focused on homodimers and not heterodimers. However, in a mixture of multiple isoforms in addition to homodimers, heterodimers are inevitably formed. Therefore, an accurate description of the kinetic parameters of individual dimerizations and thus the ability to quantify the populations of homo- and heterodimers is desired and could facilitate future work with heterodimers.
In previous years our group designed FRET assay to quantitatively determine 14-3-3 dimerization parameters, namely rate and dissociation constants. Our colleagues already characterized homodimerization of isoforms ξ, γ, ε, σ and heterodimerization of γζ and ζε as well as ζ with ζ phosphorylated at Ser58 [3-5]. In this project, we have further extended the knowledge to homodimerization of isoform η and heterodimerizations of ηζ and ηε. The main aim of this study is to compare the properties of chosen homo- and heterodimerizations and to show that heterodimers potentially account for a significant portion of the various dimer populations in tissues. We also propose the usage of a mathematical model that can, based on known kinetic parameters and given concentrations of individual isoforms, determine the concentration of all possible variants of dimers and monomers in a mixture.