Mutations of β-arrestin 2 that limit self-association also interfere with interactions with the β₂-adrenoceptor and the ERK1/2 MAPKs: Implications for β₂-adrenoceptor signalling via the ERK1/2 MAPKs

FRET (fluorescence resonance energy transfer) and co-immunoprecipitation studies confirmed the capacity of ß-arrestin 2 to self-associate. Amino acids potentially involved in direct protein-protein interaction were identified via combinations of spot-immobilized peptide arrays and mapping of surface exposure. Among potential key amino acids, Lys²⁸⁵, Arg²⁸⁶ and Lys²⁹⁵ are part of a continuous surface epitope located in the polar core between the N- and C-terminal domains. Introduction of K285A/R286A mutations into ß-arrestin 2-eCFP (where eCFP is enhanced cyan fluorescent protein) and ß-arrestin 2-eYFP (where eYFP is enhanced yellow fluorescent protein) constructs substantially reduced FRET, whereas introduction of a K295A mutation had a more limited effect. Neither of these mutants was able to promote ß₂-adrenoceptor-mediated phosphorylation of the ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPKs (mitogen-activated protein kinases). Both ß-arrestin 2 mutants displayed limited capacity to co-immunoprecipitate ERK1/2 and further spot-immobilized peptide arrays indicated each of Lys²⁸⁵, Arg²⁸⁶ and particularly Lys ²⁹⁵ to be important for this interaction. Direct interactions between ß-arrestin 2 and the ß₂-adrenoceptor were also compromised by both K285A/R286A and K295A mutations of ß-arrestin 2. These were not non-specific effects linked to improper folding of ß-arrestin 2 as limited proteolysis was unable to distinguish the K285A/R286A or K295A mutants from wild-type ß-arrestin 2, and the interaction of ß-arrestin 2 with JNK3 (c-Jun N-terminal kinase 3) was unaffected by the K285A/R286A or L295A mutations. These results suggest that amino acids important for self-association of ß-arrestin 2 also play an important role in the interaction with both the ß₂-adrenoceptor and the ERK1/2 MAPKs. Regulation of ß-arrestin 2 self-association may therefore control ß-arrestin 2-mediated ß₂-adrenoceptor-ERK1/2 MAPK signalling. © The Authors.