Modulation of apolipoprotein A-IV lipid binding by an interaction between the N and C termini.
Apolipoprotein A-IV (apoA-IV) is a 376-amino acid exchangeable apolipoprotein made in the small intestine of humans. Although it has many proposed roles in vascular disease, satiety, and chylomicron metabolism, there is no known structural basis for these functions. The ability to associate with lipids may be a key step in apoA-IV functionality. We recently identified a single amino acid, Phe(334), which seems to inhibit the lipid binding capability of apoA-IV. We also found that an intact N terminus was necessary for increased lipid binding of Phe(334) mutants. Here, we identify Trp(12) and Phe(15) as the N-terminal amino acids required for the fast lipid binding seen with the F334A mutant. Furthermore, we found that individual disruption of putative amphipathic alpha-helices 3-11 had little effect on lipid binding, suggesting that the N terminus of apoA-IV may be the operational site for initial lipid binding. We also provide three independent pieces of experimental evidence supporting a direct intramolecular interaction between sequences near amino acids 12/15 and 334. This interaction could represent a unique "switch" mechanism by which apoA-IV changes lipid avidity in vivo.
Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237.
Matthew R
MR
Tubb
Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237.
R A Gangani D
RAGD
Silva
Laboratory of Experimental Gerontology, NIA, National Institutes of Health, Baltimore, Maryland 21224.
Kevin J
KJ
Pearson
Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237.
Patrick
P
Tso
Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237.
Min
M
Liu
Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237. Electronic address: Sean.Davidson@UC.edu.
W Sean
WS
Davidson
D019943:Amino Acid Substitution; D000596:Amino Acids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001054:Apolipoproteins A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002914:Chylomicrons / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007421:Intestine, Small / Q000378:metabolism; D050356:Lipid Metabolism / Q000235:genetics; D008055:Lipids / Q000737:chemistry; D020125:Mutation, Missense; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D012527:Satiation; D014652:Vascular Diseases / Q000235:genetics / Q000378:metabolism
D000596:Amino Acids; D001054:Apolipoproteins A; D002914:Chylomicrons; D008055:Lipids; C022205:apolipoprotein A-IV