Sphingomyelinase acting as a perturbator of membrane composition and structure

MARIA L. FANANI; BRUNO MAGGIO

Puerto Madryn

Conferencia; XLVI Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular SAIB; 2010

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular SAIB

Sphingomyelinase (SMase)-induced ceramide (Cer)-enriched domains in a lipid monolayer are shown to result from an out-of-equilibrium situation. This is induced by a change of composition caused by the enzymatic production of Cer in a sphingomyelin (SM) monolayer that leads to a fast SM/Cer demixing into a liquid-condensed (LC) Cer-enriched and a liquid-expanded (LE) SM-enriched phases. The morphological evolution of Cer-enriched domains shows domain shape annealing from branched to rounded shapes after quenching of SMase activity. The fast phase separation causes a transient enrichment of Cer into LC domains. As a consequence, higher intradomain repulsion leads to transient branched structures that relax to rounded shapes by decreasing the proportion of Cer in the domain. Sphingomyelinase action on membranes brings attention to the complex dynamics of lipid interfaces where several time-dependent events occur in a narrow range of space (nm-m) and time (s to min). The resultant membrane structure is consequence of the interrelation of events such as substrate degradation rate, product diffusion, lipid demixing, phase nucleation rate and slow diffusion of lipids in the LC phase. In this context, the fast action of SMase can be taken as a compositional perturbation that brings about important consequences for the structural dynamics.