title: Bidirectional control of sphingomyelinase activity and surface topography in lipid monolayers.
abstract: Lipid lateral organization is increasingly found to modulate membrane-bound enzymes. We followed in real time the reaction course of sphingomyelin (SM) degradation by Bacillus cereus sphingomyelinase (SMase) of lipid monolayers by epifluorescence microscopy. There is evidence that formation of ceramide (Cer), a lipid second messenger, drives structural reorganization of membrane lipids. Our results provide visual evidence that SMase activity initially alters surface topography by inducing phase separation into condensed (Cer-enriched) and expanded (SM-enriched) domains. The Cer-enriched phase grows steadily as the reaction proceeds at a constant rate. The surface topography derived from the SMase-driven reaction was compared with, and found to differ from, that of premixed SM/Cer monolayers of the same lipid composition, indicating that substantial information content is stored depending on the manner in which the surface was generated. The long-range topographic changes feed back on the kinetics of Smase, and the onset of condensed-phase percolation is temporally correlated with a rapid drop of reaction rate. These observations reveal a bidirectional influence and communication between effects taking place at the local molecular level and the supramolecular organization. The results suggest a novel biocatalytic-topographic mechanism in which a surface enzymatic activity can influence the function of amphitropic proteins important for cell function.
authors.affiliation: Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina.
authors.forename: María Laura
authors.initials: ML
authors.lastname: Fanani
authors.forename: Steffen
authors.initials: S
authors.lastname: Härtel
authors.forename: Rafael G
authors.initials: RG
authors.lastname: Oliveira
authors.forename: Bruno
authors.initials: B
authors.lastname: Maggio
mesh_terms: D000818:Animals; D001409:Bacillus cereus / Q000737:chemistry; D001923:Brain Chemistry; D002232:Carbocyanines / Q000737:chemistry*; D002417:Cattle; D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure; D002518:Ceramides / Q000138:chemical synthesis / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D046911:Macromolecular Substances; D008560:Membrane Fluidity; D021962:Membrane Microdomains / Q000737:chemistry; D008567:Membranes, Artificial; D008856:Microscopy, Fluorescence / Q000379:methods; D008968:Molecular Conformation; D011312:Pressure; D013108:Sphingomyelin Phosphodiesterase / Q000737:chemistry*; D013109:Sphingomyelins / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D002232:Carbocyanines; D002518:Ceramides; D008055:Lipids; D046911:Macromolecular Substances; D008567:Membranes, Artificial; D013109:Sphingomyelins; C072024:carbocyanine dye DiIC12(3); D013108:Sphingomyelin Phosphodiesterase