Investigation of Lysozyme-Chitobioside Interactions Using Synchronous Luminescence and Lifetime Measurements

Beside their ability to disrupt the outer membranes of some microorganisms, lysozymes also experience interactions with chitins or their fluorescent analogs. It has been well established that chitins bind to the cleft of lysozymes and the subsites of the location of the different N-acetylglucosamines that are parts of chitins have been identified. Moreover, it has been well documented that a 1,4--bond must be located between subsite D and subsite E to be cleaved. Nevertheless, a better understanding of the biophysical and biochemical processes is needed.In this paper, pulsed fluorescence was used to further investigate the mechanism by which the binding of fluorescent analogs of chitin (4-methylumbelliferyl chitobiose and 4-methylumbelliferyl chitotriose) to hen egg-white lysozyme results in an increase of their fluorescence intensity. Although such an increase is not observed when these chitobiosides bind to turkey egg-white lysozyme, synchronous fluorescence techniques show that this binding induces a quenching of the native fluorescence of both these proteins.The findings of this study, associated with previously published cyrstallographic data allow us to suggest that the system lysozyme-chitobioside partitions in two three-dimensional conformational states: an enzymatic active conformation and a storage conformation. These states are separated by an energy barrier, with the storage conformation being more populated than the enzymatic active conformation below 45°C.