STRUCTURE OF HEXAMERIC BUNDLES OF BETA-AMINO ACID PEPTIDE U1F

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. U1F: b3Glu-b3Leu-b3Orn-b3Phe-b3Leu-b3Asp-b3Phe-b3Leu-b3Orn-b3Orn-b3Leu-b3Asp where b3Xxx refers to the 3-substituted beta-amino acid corresponding to the homoligation product of alpha-amino acid Xxx. Orn = ornithine. We have synthesized U1F, a beta-amino acid dodecapeptide, which folds cooperatively to form a stable homohexamer in water. Its folding has been characterized by deuterium exchange NMR experiments and circular dichroism measurments. Its oligomeric state in solution was assigned to be a hexamer by analytical ultracentrifugation. We have obtained crystals which diffract to approximately 3 angstroms on our home source (Yale Center for Structural Biology). We have assigned the space group to P42212 and the unit cell dimensions to 43 X 43 X 75 angstroms. This is consistent with a unit cell containing a hexameric U1F bundle. At CHESS, we hope to obtain significantly higher resolution diffraction data, which is currently limited by crystal size and source intensity. We are screening derivatives for phasing on our home source and may also bring confirmed derivatives for high resolution data collection. The hexameric U1F represents the first example of ternary structure in a molecule composed of unnatural beta-amino acids. U1F is also significant because it is one of the smallest (12mer) quaternary structures, natural or unnatural, to display a cooperative folding transition. U1F has been designed to fold and oligomerize based on principles gleaned from studies of beta-peptide secondary structure and leucine zipper ternary structure. Rationally designed folded polymers represent an important demonstration of our understanding of the forces which govern folding in both natural (i.e. protein) and unnatural systems. Therefore, we expect that a high resolution structure of U1F will be of great general interest to both the chemistry and biology communities. Dr. Petersson received his Ph.D. studying protein structure and function through synthetic amino acid incorporation in the labs of Dennis Dougherty at Caltech. Dr. Daniels received his Ph.D. studying DNA repair enzymes through x-ray crystallography in the labs of John Tainer at Scripps.