Expression and purification of the recombinant full-length retinoblastoma protein and characterisation of its interaction with the oncoprotein HDM2

Retinoblastoma (Rb) was the first tumour suppressor factor described, and it is dysfunctional in several types of cancers. Structurally, Rb is a very large, multifunctional protein organized in different domains connected by intrinsically disordered regions. Due to the complex structure of Rb, biochemical manipulation is difficult. The Rb protein has been implicated in many different cellular processes, such as the cell cycle control, senescence and even apoptosis. The activity of Rb is regulated by phosphorylation, and many different sites of phosphorylation have been described. However, the oncoprotein HDM2, can promote Rb degradation by the proteasome. This form of Rb regulation is largely unknown. Here we report the expression and purification of the full-length Rb protein and its phosphomimetic form, Rb(S567D), in a recombinant system. We also produced and purified the HDM2 protein and its phosphomimetic mutant, HDM2(5395D). The proteins interacted strongly when we used the phosphomimetic mutants, mimicking damaged DNA conditions. The expression of the proteins in E. coli allowed us to control the phosphorylation status of the proteins.