UC San Diego

Intrinsically disordered regions (IDRs) within proteins have recently been established as having vital functions in both protein recognition and signal transduction. An additional level of complexity is introduced by post- translational modifications, which often times fine-tune the function of IDRs. I have focused on two main systems involving post-translational modifications in IDRs. First, I explored the effect of hydroxylation on the stability and function of IκBα. Contrary to the speculation that the hydroxylation has functional consequences, we did not observe changes in "foldedness" (via H/D exchange mass spectrometry), binding to NF[kappa]B (via surface plasmon resonance), or stability (via proteosome degradation experiments). I also explored the interactions among the IDRs of LRP-CT, AICD, and Fe65, and how post-translational modifications affect these interactions. The intracellular tail of the low-density receptor-related protein (LRP-CT) has been shown to modulate the processing of APP to A[beta], the main component found in Alzheimer's disease brain plaques. The intracellular domain of APP (AICD) and LRP-CT can be linked via the adapter protein Fe65. The PID1 domain of Fe65 can bind LRP-CT and the PID2 domain of Fe65 can bind AICD. The phosphorylation of AICD did not affect the binding of AICD to Fe65, yet the phosphorylation of LRP-CT was necessary for binding to Fe65 and for the trimeric interaction between LRP-CT, Fe65, and AICD to occur. Interestingly, the interaction between the Fe65 PID1 domain and the NPXY motif of LRP-CT is predicted to be phosphorylation-independent because Fe65 PID1 belongs to the Dab-like family of PID domains, in which binding does not depend on phosphorylation. Fe65 PID1 is thus the first Dab-like PID domain identified to bind an NPXY motif in a tyrosine phosphorylation-dependent manner