title: From protein structure to function via single crystal optical spectroscopy.
abstract: The more than 100,000 protein structures determined by X-ray crystallography provide a wealth of information for the characterization of biological processes at the molecular level. However, several crystallographic "artifacts," including conformational selection, crystallization conditions and radiation damages, may affect the quality and the interpretation of the electron density maps, thus limiting the relevance of structure determinations. Moreover, for most of these structures, no functional data have been obtained in the crystalline state, thus posing serious questions on their validity in infereing protein mechanisms. In order to solve these issues, spectroscopic methods have been applied for the determination of equilibrium and kinetic properties of proteins in the crystalline state. These methods are UV-vis spectrophotometry, spectrofluorimetry, IR, EPR, Raman, and resonance Raman spectroscopy. Some of these approaches have been implemented with on-line instruments at X-ray synchrotron beamlines. Here, we provide an overview of investigations predominantly carried out in our laboratory by single crystal polarized absorption UV-vis microspectrophotometry, the most applied technique for the functional characterization of proteins in the crystalline state. Studies on hemoglobins, pyridoxal 5'-phosphate dependent enzymes and green fluorescent protein in the crystalline state have addressed key biological issues, leading to either straightforward structure-function correlations or limitations to structure-based mechanisms.
authors.affiliation: Department of Neurosciences, University of Parma Parma, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Ronda
authors.affiliation: Department of Pharmacy, University of Parma Parma, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Bruno
authors.affiliation: Department of Neurosciences, University of Parma Parma, Italy ; National Institute of Biostructures and Biosystems Rome, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Bettati
authors.affiliation: Elettra Sincrotrone Trieste Trieste, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Storici
authors.affiliation: Department of Pharmacy, University of Parma Parma, Italy ; National Institute of Biostructures and Biosystems Rome, Italy ; Institute of Biophysics, Consiglio Nazionale delle Ricerche Pisa, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Mozzarelli
keywords: X-ray crystallography; conformational changes; metastable intermediate; microspectrophotometry; protein crystal; structure-function relationship; synchrotron source