INTERACTIONS AND MOLECULAR-STRUCTURE OF CARDIOLIPIN AND BETA(2)-GLYCOPROTEIN-1 (BETA(2)-GP1)

beta 2-GP1 is a serum protein which influences binding of anticardioli pin antibodies to cardiolipin, may influence induction of these antibo dies in animals and may play a role in anticardiolipin-mediated thromb osis. Various investigators have proposed that when beta(2)-GP1 binds cardiolipin, structural alterations occur in one or both molecules, re sulting in exposure of new epitopes for anticardiolipin binding, but t here has been no proof that such alterations occur. Utilizing Fourier transform infrared spectroscopy, this study analysed the structure of cardiolipin and beta(2)-GP1 alone, then mixed with each other. For pur e cardiolipin, analysis of the CH2 stretching, scissoring and carbonyl bands suggested this molecule assumes a hexagonal crystal lattice pac king structure in both anhydrous and aqueous samples. Based on the sec ond derivative analysis of the amide 1 band from the beta(1)-GP1 prote in backbone, as well as Fourier self-deconvolution and curve fit algor ithms, beta 2-GP1 was calculated to contain 18% turns, 37% alpha-helix , and 45% beta-sheet structure. beta(2)-GP1 binding with cardiolipin r esults in a significant change in the conformation as well as geometry of the lipid and protein components. This is indicated by a broadenin g of the CH stretching band and a marked shift in intensity of the car bonyl band of cardiolipin, indicating less hydrogen bonding. There was a decrease in beta-sheet structure of beta(2)-GP1 from 46% to 23% and appearance of 26% to 28% random structure. These findings indicate th at mixing beta(2)-GP1 with cardiolipin results in profound changes in both molecules which might explain the effect of beta(2)-GP1 on antica rdiolipin binding activity.