Biochemistry Seminar - Dr. Ansgar Siemer
Dr. Ansgar Siemer
Department of Chemistry, Columbia University, New York
鈥淪olid-State NMR Investigations on Protein-Solvent Interactions and Prion Proteins鈥�
听
Solid-state NMR is a new tool in structural biology used to investigate protein systems at atomic resolution that are inaccessible with other techniques such as X-ray crystallography and liquid-state NMR. I will present recent solid-state NMR results on two of such systems:
The first system is antifreeze proteins (AFPs) and their ice binding properties. Their ice affinity distinguishes AFPs from other soluble proteins, which are, even in the presence of ice, surrounded by a hydration shell. We identified the ice-binding surface of type III AFP (AFP听III) by measuring 13C chemical shift perturbations. Furthermore, ice-protein cross relaxation as well as cross saturation data confirmed that AFP听III is in direct contact to ice. Using water-protein correlation spectra, we showed that AFP听III keeps parts of its hydration shell while binding to ice. Frozen solution solid-state NMR is, therefore, suitable to measure protein-ice interaction but also the interaction of proteins with their hydration shell in general.
The second system is prion proteins in their infective amyloid conformation. In contrast to disease related prions, functional prions are characterized by a gain of function and are beneficial in their aggregated prion conformation. I will present structural data on two of such prions: The first example is HET-s, a prion from a filamentous fungus. HET-s gave solid-state NMR spectra of such high resolution that we were able to determine the atomic resolution structure of the HET-s amyloid fibrils. The second example is the neuronal isoform of CPEB from the sea snail Aplysia, a key player in long-term memory, which is only active in its aggregated prion conformation. Although samples of CPEB did not give the same spectral quality as compared to HET-s, they held some surprises and we were able to determine the dynamical and structural heterogeneity of amyloid fibrils formed by CPEB.
Mandatory for Graduate Students