Family-Wide Characterization of Histone Binding Abilities of PHD Domains of AL Proteins in Arabidopsis thaliana

Alfin1-like (AL) is a family of proteins homologous to the alfalfa Alfin1 in plant and bears an Alfin domain and a PHD domain at their N- and C-terminus, respectively. There are 7 AL proteins in Arabidopsis, and the PHD domains of most AL proteins are reported to bind to histone H3K4me3. Here we reported gene cloning, protein expression and purification of the PHD domains of all the AL family proteins in Arabidopsis. We then systematically characterized their histone binding abilities by quantitative isothermal titration calorimetry and fluorescence polarization binding assays. Our binding results indicate that all the PHD domains of the AL proteins bind to the histone H3K4me3 peptide with varying methylation state preference and binding affinities. Our study presented here provides the foundation for further studies of the peptide state-specific recognition by PHD domains of AL proteins.