Characterizing Changes in Peptide Binding Specificity as S100 Proteins Evolve Sarina Pollat1, Luke Wheeler2, Michael Harms2 University of New Mexico1, University of Oregon2 Specific Protein-Protein Interactions Can Change Over Time fix maldi tof parameters? Pdb 2Jtt 1k96 Results and Conclusions 1. Clone DNA into vector and transform into E. coli 2. Induce bacteria to express protein of interest 3. Purify protein using Fast Protein Liquid Chromatography Kd (uM) NCX1 Proteins can have many binding partners in a biological environment, which may be a subset of the total possible binding set. Specificity defines the interactions within the binding set. Changing specificity can alter the binding members over evolution. We are studying how specificity has changed over the course of evolution by using two members of the Ca2+ -binding S100 protein family, S100A5 and S100A6, as experimental models. Evolutionary changes in the amino acid sequence along the S100A5 and S100A6 lineages have led to each protein developing a different specificity for their binding partners. The focus of this research is to determine if the human S100A5 and human S100A6 binding patterns are representative of other species in their clades. siP human PCR product Selected vector mouse S100A5 Ancestor A5 tas. devil Target 1 Target 2 alligator human Anc A5/A6 Recombinant vector Protein mouse Plac tas. devil S100A6 Target 3 alligator Ancestor A6 Target 4 chicken Target 5 Recombinant E. coli Figure 1A. A protein’s set of binding partners Figure 1B. S100 Protein structure; PDB 2JTT & 1K96 The siP peptide binds to both gA6 and mA6, leading us to believe that humans are representative of the orthologs in the s100A6 clade. Binding of the siP peptide is conserved in diverse species. The NCX1 peptide binds to mA5, suggesting that binding of this peptide is conserved in the S100A5 clade. Bacterial lysate containing over expressed protein Purified protein Plated on LB + antibiotics Kd (uM) siP NCX1 4. We measured the binding of peptides with purified S100A5 and S100A6 orthologous proteins using isothermal titration calorimetry (ITC) Future Directions human Ancestor A5 Kd (uM) S100A5 Ancestor A5/A6 NCX1 siP human S100A6 human Ancestor A6 mouse ? S100A5 Figure 2. Human S100A5 and Human S100A6 are observed to have varying binding specificities for two known peptides, siP and NCX1. A dark colored diamond or rectangle is representative of strong binding, while a white color is representative of no binding. Ancestor A5 tas. devil ? ? alligator ? ? human Anc A5/A6 mouse ? tas. devil ? ? S100A6 alligator ? ? Ancestor A6 chicken ? Objectives Continue peptide binding experiments for both peptides (siP, NCX1) across all orthologs and paralogs to identify a pattern of specificity. Expand the orthologous proteins (tasmanian devil, alligator) and continue peptide binding experiments with them. Use other isolated peptides and test binding across all orthologs and paralogs. To better characterize how specificity for binding partners evolved, we will trace specificity for two known biological targets, siP and NCX1, across orthologs and paralogs To do this we must obtain purified proteins from a variety of organisms by cloning, expressing, and purifying them. We can then do binding experiments with the purified proteins and isolated peptides. Figure 3. Binding of known concentration of siP peptide to known concentration of purified chicken S100A6 protein. Figure 4. Binding of known concentration of siP peptide to known concentration of purified mouse S100A6 protein. Figure 5. Binding of known concentration of siP peptide to known concentration of purified chicken S100A6 protein. Acknowledgements Harms Lab: Michael Harms, Luke Wheeler, Andrea Loes, Zach Sailer, Joseph Harman, Anneliese Morrison, Bram Rickett, Ran Shi University Of Oregon SPUR, funded by NSF REU in Molecular Biosciences at the University of Oregon: NSF DBI/BIO 1460735