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Dipartimento di Fisica e Scienze della Terra

Subdiffraction localization of a fluorescent photosensitizer in bacterial cells

 

Delcanale, P.; Pennacchietti, F.; Maestrini, G.; Rodríguez-Amigo, B.; Bianchini, P.; Diaspro, A.; Iagatti, A.; Patrizi, B.; Foggi, P.; Agut, M.; Nonell, S.; Abbruzzetti, S.; Viappiani, C.Scientific Reports 2015, 5, 15564.

 

Antibacterial treatments based on photosensitized production of reactive oxygen species is a promising approach to address local microbial infections. Given the small size of bacterial cells, identification of the sites of binding of the photosensitizing molecules is a difficult issue to address with conventional microscopy. We show that the excited state properties of the naturally occurring photosensitizer hypericin can be exploited to perform STED microscopy on bacteria incubated with the complex between hypericin and apomyoglobin, a self-assembled nanostructure that confers very good bioavailability to the photosensitizer. Hypericin fluorescence is mostly localized at the bacterial wall, and accumulates at the polar regions of the cell and at sites of cell wall growth. While these features are shared by Gram-negative and Gram-positive bacteria, only the latter are effectively photoinactivated by light exposure.
 
 

Experimental basis for a new allosteric model for multisubunit proteins

 

Viappiani C, Abbruzzetti S, Ronda L, Bettati S, Henry ER, Mozzarelli A, Eaton WA (2014) Experimental basis for a new allosteric model for multisubunit proteins. Proc Natl Acad Sci USA, 111, 12758-12763.

 

Although the theoretical model of Monod, Wyman, and Changeux (MWC) is one of the most influential and highly cited theoreticalmodels in bioscience, it fails to explain allosteric effects in hemoglobin, the paradigm of allostery, because their model considers only quaternary preequilibria. By using a new kind of laser photolysis experiment, measurements of ligand rebinding kinetics for transient hemoglobin conformations trapped by encapsulation in silica gels support the simplest possible extension of the MWC allosteric model to include tertiary in addition to quaternary conformational preequilibria. While the MWC model provides a qualitative explanation for allostery in many multisubunit proteins, quantitative analysis will most probably require the extension used here to explain our new results.