Heparin binding stabilizes the membrane-bound form of cobra cardiotoxin.
It has been shown previously that the long chain fragments of heparin bind to the beta-strand cationic belt of the three-finger cobra cardiotoxin (or cytotoxin, CTX) and hence enhance its penetration into phospholipid monolayer under physiological ionic conditions. By taking lysophosphatidylcholine (LPC) micelles as a membrane model, we have shown by (1)H NMR study that the binding of heparin-derived hexasaccharide (Hep-6) to CTX at the beta-strand region can induce conformational changes of CTX near its membrane binding loops and promote the binding activity of CTX toward LPC. The Fourier-transform infrared spectra and NMR nuclear Overhauser effect of Hep-6.CTX and CTX.LPC complex in aqueous buffer also supplemented the aforementioned observation. Thus, the detected conformational change may presumably be the result of structural coupling between the connecting loops and its beta-strands. This is the first documentation of results showing how the association of hydrophilic carbohydrate molecules with amphiphilic proteins can promote hydrophobic protein-lipid interaction via the stabilization of its membrane-bound form. A similar mechanism involving tripartite interactions of heparin, protein, and lipid molecules may be operative near the extracellular matrix of cell membranes.
Sue
Shih-Che
SC
Department of Life Sciences, National Tsing Hua University, Hsinchu 30043, Taiwan.
Chien
Kun-Yi
KY
Huang
Wei-Ning
WN
Abraham
Joseph K
JK
Chen
Kuan-Ming
KM
Wu
Wen-guey
WG
D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism*; D004179:Cobra Cardiotoxin Proteins / Q000737:chemistry* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D017815:Elapidae; D005109:Extracellular Matrix / Q000378:metabolism; D006493:Heparin / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008055:Lipids / Q000737:chemistry; D008244:Lysophosphatidylcholines / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D008958:Models, Molecular; D010743:Phospholipids / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
D004179:Cobra Cardiotoxin Proteins; D008055:Lipids; D008244:Lysophosphatidylcholines; D008823:Micelles; D010743:Phospholipids; D006493:Heparin