Phosphatidylinositol (3,4,5)-trisphosphate binds to sortilin and competes with neurotensin: Implications for very low density lipoprotein binding.
Sortilin is a multi-ligand sorting receptor that interacts with B100-containing VLDL and LDL as well as other ligands including neurotensin (NT). The current study investigates the hypothesis that phosphatidylinositol (3,4,5)-trisphosphate (PIP3) generated downstream of insulin action can directly bind to sortilin. NT binds to sortilin at a well characterized site via its carboxy terminus (C-term). Using a crystal structure of human sortilin (hsortilin), PIP3 is predicted to bind at this C-term site. Binding of PIP3 to hsortilin is demonstrated using surface plasmon resonance (SPR) flowing PIP3 nanodiscs over immobilized hsortilin. Studies were performed using SPR where dibutanoyl PIP3 is shown to compete with NT for sortilin binding. Rat VLDL and LDL were evaluated for PIP3 content immunologically using monoclonal antibodies directed against PIP3. Rat plasma VLDL contained three times more immunoreactive PIP3 than LDL per μg of protein. Because VLDL contains additional ligands that bind sortilin, to distinguish specific PIP3 binding, we used PIP3 liposomes. Liposome floatation assays were used to demonstrate PIP3 liposome binding to sortilin. Using SPR and immobilized hsortilin, the C-term NT tetrapeptide (P-Y-I-L) is shown to bind to hsortilin. A compound (cpd984) was identified with strong theoretical binding to the site on sortilin involved in NT N-terminal binding. When cpd984 is co-incubated with the tetrapeptide, the affinity of binding to sortilin is increased. Similarly, the affinity of PIP3 liposome binding increased in the presence of cpd984. Overall, results demonstrate that sortilin is a PIP3 binding protein with binding likely to occur at the C-term NT binding site. The presence of multiple ligands on B100-containing lipoproteins, VLDL and LDL, raises the interesting possibility for increased interaction with sortilin based on the presence of PIP3.
Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
Robert P
RP
Sparks
Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, NY 14642, USA.
Jermaine L
JL
Jenkins
Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
Gregory E
GE
Miner
Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
Yan
Y
Wang
Department of Chemistry, University of South Florida, Tampa, FL 33520, USA.
Wayne C
WC
Guida
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA.
Charles E
CE
Sparks
Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
Rutilio A
RA
Fratti
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA. Electronic address: Janet_Sparks@urmc.rochester.edu.
Janet D
JD
Sparks
D033942:Adaptor Proteins, Vesicular Transport / Q000737:chemistry*; D000818:Animals; D001665:Binding Sites; D003198:Computer Simulation; D006801:Humans; D008079:Lipoproteins, VLDL / Q000097:blood / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D009496:Neurotensin / Q000737:chemistry*; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry*; D010716:Phosphatidylinositols / Q000737:chemistry; D011485:Protein Binding; D000072417:Protein Domains; D051381:Rats; D017207:Rats, Sprague-Dawley; D020349:Surface Plasmon Resonance; D000099183:Sortilin
D033942:Adaptor Proteins, Vesicular Transport; D008079:Lipoproteins, VLDL; D008081:Liposomes; D009496:Neurotensin; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D000099183:Sortilin; C060974:phosphatidylinositol 3,4,5-triphosphate
Neurotensin; Sortilin; Surface plasmon resonance; VLDL-B100
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