Fig 1: GRKs differentially regulate ?-secretase activity by mediating an APH1A phosphorylation barcode(A) GRKs mediate APH1A phosphorylation within ICL2 and the C terminus of APH1A to regulate ßarr2 recruitment via interactions between the ßarr2 finger loop domain and the cytoplasmic TM core (ICL2/3) of APH1A. In turn, ßarr2 recruitment to APH1A leads to ?-secretase cleavage of APP-C99 and the generation of Aß peptides.(B) In GRK2 KO cells, APH1A ICL2 phosphorylation at both S105 and S110 is elevated relative to control cells. The ?-secretase complex exhibits increased activity and cleavage of APP-C99.(C) In GRK3 KO and GRK5 KO cells, APH1A displays reduced levels of ICL2 phosphorylation at S103 and S110 relative to control cells. The ?-secretase complex exhibits decreased activity and cleavage of APP-C99.(D) In GRK6 KO cells, APH1A phosphorylation at S110 alone is elevated relative to control cells. The ?-secretase activity and Aß generation are unaffected relative to control cells. We hypothesize that changes in the phosphorylation barcode affect both the extent of ßarr2 recruitment to APH1A and the APH1A-ßarr2 conformation following binding. We predict the positioning of H171 and H197 in APH1A is altered by ßarr2 engagement, which affects recognition and cleavage of APP-C99. The phosphorylation sites highlighted in red and blue indicate elevated or reduced levels of phosphorylation, respectively, relative to control (or basal) levels of phosphorylation at the sites highlighted in yellow. The figure was created with BioRender.com.