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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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Far-ultraviolet circular dichroism spectra of (A) apelin-12 and (B) apelin-17 in buffer, SDS micelles, DPC micelles, and LPPG micelles alongside the difference spectrum between LPPG and the buffer. Spectropolarimetry (sliding-window (eq 1) averaged blank-subtracted averages of three replicates) was performed at 35 °C in 20 mM phosphate buffer at pH 7.00 ± 0.05.
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fig1: Far-ultraviolet circular dichroism spectra of (A) apelin-12 and (B) apelin-17 in buffer, SDS micelles, DPC micelles, and LPPG micelles alongside the difference spectrum between LPPG and the buffer. Spectropolarimetry (sliding-window (eq 1) averaged blank-subtracted averages of three replicates) was performed at 35 °C in 20 mM phosphate buffer at pH 7.00 ± 0.05.

Mentions: The far-ultraviolet (far-UV) CD spectra from 260 to 190 nm of both apelin-12 and apelin-17 in buffer and in the presence of SDS, DPC, or LPPG micelles are shown in Figure 1. For any given condition, the CD spectra for both apelin-12 and apelin-17 have similar features. As we have previously described,(15) the spectra for both apelin-12 and apelin-17 in buffer at 35 °C are random coil(41) in nature. This primarily random coil spectrum is convoluted with positive bands at 195 and 218 nm, most likely attributable to the 1B and 1La transitions42,43 of the C-terminal phenylalanine.(15) For both apelin-12 and apelin-17, DPC micelles do not strongly perturb the CD spectrum relative to the buffer (Figure 1). In contrast, dramatic spectral changes occur with both apelin isoforms in the presence of either SDS or LPPG micelles. The CD spectra with these micelles present are convoluted by an α-helix-like band pattern (difference spectra in Figure 1), which may be attributed either to formation of the α-helical secondary structure(41) or to the formation of β-turns.44,45


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

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

Far-ultraviolet circular dichroism spectra of (A) apelin-12 and (B) apelin-17 in buffer, SDS micelles, DPC micelles, and LPPG micelles alongside the difference spectrum between LPPG and the buffer. Spectropolarimetry (sliding-window (eq 1) averaged blank-subtracted averages of three replicates) was performed at 35 °C in 20 mM phosphate buffer at pH 7.00 ± 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: Far-ultraviolet circular dichroism spectra of (A) apelin-12 and (B) apelin-17 in buffer, SDS micelles, DPC micelles, and LPPG micelles alongside the difference spectrum between LPPG and the buffer. Spectropolarimetry (sliding-window (eq 1) averaged blank-subtracted averages of three replicates) was performed at 35 °C in 20 mM phosphate buffer at pH 7.00 ± 0.05.
Mentions: The far-ultraviolet (far-UV) CD spectra from 260 to 190 nm of both apelin-12 and apelin-17 in buffer and in the presence of SDS, DPC, or LPPG micelles are shown in Figure 1. For any given condition, the CD spectra for both apelin-12 and apelin-17 have similar features. As we have previously described,(15) the spectra for both apelin-12 and apelin-17 in buffer at 35 °C are random coil(41) in nature. This primarily random coil spectrum is convoluted with positive bands at 195 and 218 nm, most likely attributable to the 1B and 1La transitions42,43 of the C-terminal phenylalanine.(15) For both apelin-12 and apelin-17, DPC micelles do not strongly perturb the CD spectrum relative to the buffer (Figure 1). In contrast, dramatic spectral changes occur with both apelin isoforms in the presence of either SDS or LPPG micelles. The CD spectra with these micelles present are convoluted by an α-helix-like band pattern (difference spectra in Figure 1), which may be attributed either to formation of the α-helical secondary structure(41) or to the formation of β-turns.44,45

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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