Phospholipid membrane restructuring induced by saposin C: a topographic study using atomic force microscopy

The enzymatic activity of glucosylceramidase depends on the presence of sap osin C (Sap C) and acidic pbospholipid-containing membranes. In order to de lineate the mechanism underlying Sap C stimulation of the enzyme activity, it is important to understand how Sap C interacts with phospholipid membran es. We studied the dynamic process of Sap C interaction with planar phospho lipid membranes, in real time, using atomic force microscopy (AFM). The pho spholipid membrane underwent restructuring upon addition of Sap C. The topo graphic characteristics of the membrane restructuring include the appearanc e of patch-like new features, initially emerged at the edge of phospholipid membranes and extended laterally with time. Changes in the image contrast of the phospholipid membrane observed after the Sap C addition indicate tha t a new phase of lipid-protein structure has formed during membrane restruc turing. The process of membrane restructuring is dynamic, commencing shortl y after Sap C addition, and continuing throughout the duration of AFM imagi ng (about 30 min, sometimes over 1 h). This study demonstrated the potentia l of AFM real-time imaging in studying protein-membrane interactions. (C) 2 001 Published by Elsevier Science B.V. on behalf of the Federation of Europ ean Biochemical Societies.