Membrane-anchoring and charge effects in the interaction of myelin basic protein with lipid bilayers studied by site-directed spin labeling.
Myelin basic protein (MBP) maintains the compaction of the myelin sheath in the central nervous system by anchoring the cytoplasmic face of the two apposing bilayers and may also play a role in signal transduction. Site-directed spin labeling was done at eight matching sites in each of two recombinant murine MBPs, qC1 (charge +19) and qC8 charge (+13), which, respectively, emulate the native form of the protein (C1) and a post-translationally modified form (C8) that is increased in multiple sclerosis. When interacting with large unilamellar vesicles, most spin-labeled sites in qC8 were more mobile than those in qC1. Depth measurement via continuous wave power saturation indicated that the N-terminal and C-terminal sites in qC1 were located below the plane of the phospholipid headgroups. In qC8, the C-terminal domain dissociated from the membrane, suggesting a means by which the exposure of natural C8 to cytosolic enzymes and ligands might increase in vivo in multiple sclerosis. The importance of two Phe-Phe pairs in MBP to its interactions with lipids was investigated by separately mutating each pair to Ala-Ala. The mobility at F42A/F43A and especially F86A/F87A increased significantly. Depth measurements and helical wheel analysis indicated that the Phe-86/Phe-87 region could form a surface-seeking amphipathic alpha-helix.
Bates
Ian R
IR
Department of Molecular Biology and Genetics and Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Boggs
Joan M
JM
Feix
Jimmy B
JB
Harauz
George
G
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D008051:Lipid Bilayers / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009103:Multiple Sclerosis / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D004676:Myelin Basic Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins; D013113:Spin Labels; D055672:Static Electricity; D013329:Structure-Activity Relationship
D008051:Lipid Bilayers; D004676:Myelin Basic Protein; D010446:Peptide Fragments; D020033:Protein Isoforms; D011994:Recombinant Proteins; D013113:Spin Labels