Sphingomyelinase-induced domain shape relaxation driven by out-of-equilibrium changes of composition.
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, SM-enriched phases. The morphological evolution and kinetic dependence of Cer-enriched domains is studied under continuous observation by epifluorescence microscopy. Domain shape annealing is observed from branched to rounded shapes after SMase activity quenching by EDTA, with a decay halftime of approximately 10 min. An out-of-equilibrium fast domain growth is not the determinant factor for domain morphology. Domain shape rearrangement in nearly equilibrium conditions result from the counteraction of intradomain dipolar repulsion and line tension, according to McConnell's shape transition theory. Phase separation causes a transient compositional overshoot within the LC phase that implies an increased out-of-equilibrium enrichment of Cer into the LC domains. As a consequence, higher intradomain repulsion leads to transient branched structures that relax to rounded shapes by lowering the proportion of Cer in the domain to equilibrium values. The fast action of SMase can be taken as a compositional perturbation that brings about important consequences for the surface organization.
Departamento de Química Biológica, Centro de Investigaciones en Química Biológica de Córdoba, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina, Haya de Torre y Medina Allende, Ciudad Universitaria, Córdoba, Argentina. lfanani@gmail.com
Maria Laura
ML
Fanani
Luisina
L
De Tullio
Steffen
S
Hartel
Jorge
J
Jara
Bruno
B
Maggio
D000818:Animals; D001409:Bacillus cereus; D055592:Biophysical Phenomena; D002417:Cattle; D002518:Ceramides / Q000737:chemistry*; D046169:Dermoscopy; D004492:Edetic Acid / Q000737:chemistry; D007700:Kinetics; D008567:Membranes, Artificial; D008956:Models, Chemical; D044367:Phase Transition; D011487:Protein Conformation; D013108:Sphingomyelin Phosphodiesterase / Q000737:chemistry*
D002518:Ceramides; D008567:Membranes, Artificial; D004492:Edetic Acid; D013108:Sphingomyelin Phosphodiesterase