The N-terminal 17% of apoB binds tightly and irreversibly to emulsions modeling nascent very low density lipoproteins.
The N-terminal 17% of apolipoprotein B (apoB-17) readily associates with dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles (MLV) to form large (240-A diameter) discoidal particles. Because apoB is normally secreted with triacylglycerol (TAG)-rich lipoproteins, we studied the binding of apoB-17 to triolein-rich emulsions modeling nascent TAG-rich very low density-like lipoproteins. Emulsions with the following composition (by weight) were prepared: 85--89% triolein, 1.1--1.4% cholesterol, and 10--14% phosphatidylcholines (PC) including either egg yolk (EY)-, dimyristoyl (DM)-, or dipalmitoyl (DP)-PC representing (at 25 degrees C), respectively, a fluid surface, a surface at transition, and a mainly solid surface. The respective sizes were 1,260 +/- 500, 1,070 +/- 450, and 830 +/- 300 A mean diameter. The emulsions were incubated with conditioned medium containing apoB-17, and then reisolated by ultracentrifugation. Analysis of the emulsion-bound proteins by gel electrophoresis showed that all three emulsions bound primarily apoB-17. The DPPC emulsions bound more apoB-17 than EYPC or DMPC emulsions. Immunoaffinity-purified apoB-17 exhibited saturable, high affinity binding to EYPC and DPPC emulsions. The respective K(d) values were 32 +/- 23 and 85 +/- 27 nM and capacities (N) were 10 and 58 molecules of apoB-17 per particle. When apoB-17 bound to emulsions was incubated with DMPC MLV at 26 degrees C for 18 h, it remained bound to the emulsions, indicating that once bound to these emulsions it is unable to exchange off and solubilize DMPC into discs. In contrast, apoE-3 bound to emulsions dissociated from the emulsions when incubated with DMPC MLV and formed discs.Thus, apoB-17 binds strongly and irreversibly to emulsions modeling nascent lipoproteins. It therefore may play an important role in the stabilization of nascent VLDL and chylomicrons.- Herscovitz, H., A. Derksen, M. T. Walsh, C. J. McKnight, D. L. Gantz, M. Hadzopoulou-Cladaras, V. Zannis, C. Curry, and D. M. Small. The N-terminal 17% of apoB binds tightly and irreversibly to emulsions modeling nascent very low density lipoproteins. J. Lipid Res. 2001. 42: 51;-59.
Herscovitz
H
H
Department of Biophysics, Cardiovascular Institute, Center for Advanced Biomedical Research, Boston University School of Medicine, Boston, MA 02118, USA. haya@med-biophd.bu.edu
Derksen
A
A
Walsh
M T
MT
McKnight
C J
CJ
Gantz
D L
DL
Hadzopoulou-Cladaras
M
M
Zannis
V
V
Curry
C
C
Small
D M
DM
D000818:Animals; D001055:Apolipoproteins B / Q000737:chemistry / Q000378:metabolism*; D001667:Binding, Competitive; D002460:Cell Line; D004655:Emulsions / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D010713:Phosphatidylcholines / Q000378:metabolism; D011485:Protein Binding; D014304:Triolein / Q000378:metabolism
D001055:Apolipoproteins B; D004655:Emulsions; D008079:Lipoproteins, VLDL; D008081:Liposomes; D010713:Phosphatidylcholines; D014304:Triolein