title: Direct AFM observation of saposin C-induced membrane domains in lipid bilayers: from simple to complex lipid mixtures.
abstract: Saposin C (Sap C) is a small glycoprotein required by glucosylceramidase (GCase) for hydrolysis of glucosylceramide to ceramide and glucose in lysosomes. The molecular mechanism underlying Sap C stimulation of the enzyme activation is not fully understood. Here, atomic force microscopy (AFM) has been used to study Sap C-membrane interactions under physiological conditions. First, to establish how Sap C-membrane interactions affect membrane structure, lipid bilayers containing zwitterionic and anionic phospholipids were used. It was observed that Sap C induced two types of membrane restructuring effects, i.e., the formation of patch-like domains and membrane destabilization. Bilayers underwent extensive structural reorganization. To validate the biological importance of the membrane restructuring effects, interaction of Sap C with lipid bilayers composed of cholesterol, sphingomyelin, and zwitterionic and anionic phospholipids were studied. Although similar membrane restructuring effects were observed, Sap C-membrane interactions, in this case, were remarkably modulated and their effects were restricted to a limited area. As a result, nanometer-sized domains were formed. The establishment of a model membrane system will allow us to further study the dynamics, structure and mechanism of the Sap C-associated membrane domains and to examine the important role that these domains may play in enzyme activation.
authors.affiliation: Department of Cell Biology, Neurobiology, and Anatomy, College of Medicine, University of Cincinnati, 3125 Eden Ave, Cincinnati, OH 45267-0521, USA. hong.you@uc.edu
authors.forename: Hong Xing
authors.initials: HX
authors.lastname: You
authors.forename: Xiaoyang
authors.initials: X
authors.lastname: Qi
authors.forename: Lei
authors.initials: L
authors.lastname: Yu
mesh_terms: D045424:Complex Mixtures / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D021962:Membrane Microdomains / Q000737:chemistry* / Q000648:ultrastructure*; D008565:Membrane Proteins / Q000737:chemistry; D018625:Microscopy, Atomic Force; D010743:Phospholipids / Q000737:chemistry*; D049231:Saposins / Q000737:chemistry* / Q000648:ultrastructure*; D013499:Surface Properties
chemical_list: D045424:Complex Mixtures; D008051:Lipid Bilayers; D008565:Membrane Proteins; D010743:Phospholipids; D049231:Saposins