Using Histone H1 Derived Peptides to Investigate Binding Affinity and Inter-Domain Dynamics in Human Pin1

Abstract

Pin1 is an essential Peptidyl-prolyl isomerase (PPIase) that catalyzes cis-trans prolyl isomerization in proteins containing pSer/pThr-Pro motifs. It has an N-terminal WW domain that targets pSer/Thr-Pro motifs and a C-terminal PPIase domain that catalyzes isomerization. In this study, we report a novel series of chimeric peptides that has been designed to optimize binding across the inter-domain interface of Pin1. The peptide series was designed based on the binding site of the Pin1 and optimal peptide sequences analyzed in earlier studies. Specifically, we started from a sequence derived from the human Histone H1.4 sequence (KATGAApTPKKSAKW). Then, we designed a series of chimeric peptides based on this H1.4 sequence. NMR titrations were performed for each peptide using both full-length Pin1 as well as the WW domain alone. An analysis of KD values reveals complexity in the energetics of interaction between the peptide substrate, the PPIase domain, and the WW domain. 15N relaxation and residual dipolar couplings (RDCs) were used to monitor the degree to which peptide binding induced inter-domain interactions. When combined with molecular simulations, our results suggest a structural basis for how substrate binding can alter the inter-domain dynamics. Finally, we investigated whether our chimeric sequences could alter catalysis (kex) using 1H-1H EXSY NMR experiments. Interestingly, no relationship was found between kex and either peptide affinity or inter-domain interaction, suggesting a lack of allosteric control for this series of peptides. Thus, while our results suggest that peptide binding can alter the interaction between the PPIase and WW domains, altering the inter-domain interaction by itself does not appear to modulate catalysis in the PPIase domain.