Modulation of the activity of Clostridium perfringens neuraminidase by the molecular organization of gangliosides in monolayers

The activity of Clostridium perfringens neuraminidase against gangliosides GM₃, GD_1a and GM₁ was studied in lipid monolayers at the air-buffer solution interface. The enzyme activity assay against pure ganglioside monolayers is based on the markedly different molecular packing areas of the substrate gangliosides and the resulting product glycosphingolipids. This allows to control and monitor the surface pressure and the ganglioside intermolecular organization (cross-sectional packing areas and dipole potentials) in a continuous manner during the catalytic process. It was found that the rate and the extent of the enzymatic reaction depended markedly on the lateral surface pressure. In general, the activity of neuraminidase against GM₃ and GD_1a was higher at lower surface pressure. This corresponded to larger intermolecular spacings among the ganglioside molecules. Both the activity and the extent of the reaction against GM₃ were higher than toward GD_1a. GM₁ could not be degraded by the enzyme, irrespective of the surface pressure but the enzyme could interact with this ganglioside. A latency period, longer for GM₃ than for GD_1a, was observed prior to the onset of rapid degradation; this indicates that pre-catalytic steps are occurring at the interface before effective ganglioside degradation takes place. The latency period, the total amount of ganglioside degraded, and the velocity of the reaction varied with the surface pressure in different manners. Our data indicate that the different steps of the catalytic reaction occurring at the surface (i.e., substrate recognition and interfacial adsorption, catalysis, maximum extent of substrate conversion) are independently regulated by the molecular organization of the substrate gangliosides.