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Headgroup-dependent membrane catalysis of apelin-receptor interactions is likely.

Langelaan DN, Rainey JK - J Phys Chem B (2009)

Bottom Line: Type I beta-turns are initiated between R6 and L9, and a well-defined type IV beta-turn is initiated at S10.Furthermore, binding of apelin-17 to SDS micelles causes structuring of M15-F17, with no evidence for direct binding of this region to the micelles.These results are placed into the context of the membrane catalysis hypothesis for peptide-receptor binding, and a hypothetical mechanism of APJ binding and activation by apelin is advanced.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada.

ABSTRACT
Apelin is the peptidic ligand for the G-protein-coupled receptor APJ. The apelin-APJ system is important in cardiovascular regulation, fluid homeostasis, and angiogenesis, among other roles. In this study, we investigate interactions between apelin and membrane-mimetic micelles of the detergents sodium dodecyl sulfate (SDS), dodecylphosphocholine (DPC), and 1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-rac-(1-glycerol)] (LPPG). Far-ultraviolet circular dichroism spectropolarimetry and diffusion-ordered spectroscopy indicate that apelin peptides bind to micelles of the anionic detergents SDS and LPPG much more favorably than to zwitterionic DPC micelles. Nuclear magnetic resonance spectroscopy allowed full characterization of the interactions of apelin-17 with SDS micelles. Titration with paramagnetic agents and structural determination of apelin-17 in SDS indicate that R6-K12 is highly structured, with R6-L9 directly interacting with headgroups of the micelle. Type I beta-turns are initiated between R6 and L9, and a well-defined type IV beta-turn is initiated at S10. Furthermore, binding of apelin-17 to SDS micelles causes structuring of M15-F17, with no evidence for direct binding of this region to the micelles. These results are placed into the context of the membrane catalysis hypothesis for peptide-receptor binding, and a hypothetical mechanism of APJ binding and activation by apelin is advanced.

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Retained peak intensity (the error bar is the average deviation) of apelin-17 in SDS micelles with the indicated amounts of (A) 5-DSA or 16-DSA or (B) Mn2+ calculated from the intensities of the 1H−1H TOCSY peaks relative to a reference spectrum.
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fig3: Retained peak intensity (the error bar is the average deviation) of apelin-17 in SDS micelles with the indicated amounts of (A) 5-DSA or 16-DSA or (B) Mn2+ calculated from the intensities of the 1H−1H TOCSY peaks relative to a reference spectrum.

Mentions: To determine the region of apelin-17 that is interacting with anionic micelles, paramagnetic relaxation enhancement NMR spectroscopy experiments were used. The 1H−1H TOCSY peak attenuation of apelin-17 in SDS micelles with various concentrations of 5-DSA, 16-DSA, or Mn2+ is summarized in Figure 3. These reagents would be expected to attenuate the NMR signals for nuclei in the tailgroup core of the micelle (16-DSA), just below the anionic headgroup (5-DSA), or readily accessible to solution (Mn2+). For both 5-DSA and 16-DSA, there is no clear trend of peak attenuation over apelin-17, even at relatively high concentrations of paramagnetic agent, suggesting that apelin-17 does not associate in the hydrophobic core of the micelles or just below the headgroups of SDS (Figure 3A). In contrast, a clear trend in peak attenuation is observed with the titration of apelin-17 by Mn2+. At 0.25 mM Mn2+, many residues of apelin-17 show large attenuation of peak intensity, notably at the C-terminal region (Figure 3B). After titration with 1 mM Mn2+, only K1 and R6−L9 have an observable signal, indicating that these residues of apelin-17 interact most strongly with SDS micelles since they are partially shielded from the effects of Mn2+. However, even these residues are largely attenuated by Mn2+, indicating that although they interact with the micelle, they are still partially solvent exposed and very near the micelle surface, as supported by the lack of peak attenuation induced by 5-DSA or 16-DSA.


Headgroup-dependent membrane catalysis of apelin-receptor interactions is likely.

Langelaan DN, Rainey JK - J Phys Chem B (2009)

Retained peak intensity (the error bar is the average deviation) of apelin-17 in SDS micelles with the indicated amounts of (A) 5-DSA or 16-DSA or (B) Mn2+ calculated from the intensities of the 1H−1H TOCSY peaks relative to a reference spectrum.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2736645&req=5

fig3: Retained peak intensity (the error bar is the average deviation) of apelin-17 in SDS micelles with the indicated amounts of (A) 5-DSA or 16-DSA or (B) Mn2+ calculated from the intensities of the 1H−1H TOCSY peaks relative to a reference spectrum.
Mentions: To determine the region of apelin-17 that is interacting with anionic micelles, paramagnetic relaxation enhancement NMR spectroscopy experiments were used. The 1H−1H TOCSY peak attenuation of apelin-17 in SDS micelles with various concentrations of 5-DSA, 16-DSA, or Mn2+ is summarized in Figure 3. These reagents would be expected to attenuate the NMR signals for nuclei in the tailgroup core of the micelle (16-DSA), just below the anionic headgroup (5-DSA), or readily accessible to solution (Mn2+). For both 5-DSA and 16-DSA, there is no clear trend of peak attenuation over apelin-17, even at relatively high concentrations of paramagnetic agent, suggesting that apelin-17 does not associate in the hydrophobic core of the micelles or just below the headgroups of SDS (Figure 3A). In contrast, a clear trend in peak attenuation is observed with the titration of apelin-17 by Mn2+. At 0.25 mM Mn2+, many residues of apelin-17 show large attenuation of peak intensity, notably at the C-terminal region (Figure 3B). After titration with 1 mM Mn2+, only K1 and R6−L9 have an observable signal, indicating that these residues of apelin-17 interact most strongly with SDS micelles since they are partially shielded from the effects of Mn2+. However, even these residues are largely attenuated by Mn2+, indicating that although they interact with the micelle, they are still partially solvent exposed and very near the micelle surface, as supported by the lack of peak attenuation induced by 5-DSA or 16-DSA.

Bottom Line: Type I beta-turns are initiated between R6 and L9, and a well-defined type IV beta-turn is initiated at S10.Furthermore, binding of apelin-17 to SDS micelles causes structuring of M15-F17, with no evidence for direct binding of this region to the micelles.These results are placed into the context of the membrane catalysis hypothesis for peptide-receptor binding, and a hypothetical mechanism of APJ binding and activation by apelin is advanced.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada.

ABSTRACT
Apelin is the peptidic ligand for the G-protein-coupled receptor APJ. The apelin-APJ system is important in cardiovascular regulation, fluid homeostasis, and angiogenesis, among other roles. In this study, we investigate interactions between apelin and membrane-mimetic micelles of the detergents sodium dodecyl sulfate (SDS), dodecylphosphocholine (DPC), and 1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-rac-(1-glycerol)] (LPPG). Far-ultraviolet circular dichroism spectropolarimetry and diffusion-ordered spectroscopy indicate that apelin peptides bind to micelles of the anionic detergents SDS and LPPG much more favorably than to zwitterionic DPC micelles. Nuclear magnetic resonance spectroscopy allowed full characterization of the interactions of apelin-17 with SDS micelles. Titration with paramagnetic agents and structural determination of apelin-17 in SDS indicate that R6-K12 is highly structured, with R6-L9 directly interacting with headgroups of the micelle. Type I beta-turns are initiated between R6 and L9, and a well-defined type IV beta-turn is initiated at S10. Furthermore, binding of apelin-17 to SDS micelles causes structuring of M15-F17, with no evidence for direct binding of this region to the micelles. These results are placed into the context of the membrane catalysis hypothesis for peptide-receptor binding, and a hypothetical mechanism of APJ binding and activation by apelin is advanced.

Show MeSH