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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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Structure of apelin-17 bound to an SDS micelle: (A) superposition of all 80 members of the final ensemble of structures from R6 to K12 (R6−K12 colored blue, remainder green) with P7 and S10, initiation points of type I and type IV β-turns, respectively, indicated; (B) zoom of the superposition in (A) (backbone atoms green) showing cationic side chains of R6 and R8 (blue; all other side chains red) falling on the same face of apelin-17; (C) superposition of all heavy atoms of M15−F17 for all 80 ensemble members, with the backbone shown in blue and side chains colored red.
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fig5: Structure of apelin-17 bound to an SDS micelle: (A) superposition of all 80 members of the final ensemble of structures from R6 to K12 (R6−K12 colored blue, remainder green) with P7 and S10, initiation points of type I and type IV β-turns, respectively, indicated; (B) zoom of the superposition in (A) (backbone atoms green) showing cationic side chains of R6 and R8 (blue; all other side chains red) falling on the same face of apelin-17; (C) superposition of all heavy atoms of M15−F17 for all 80 ensemble members, with the backbone shown in blue and side chains colored red.

Mentions: Independent of this, the ensemble of apelin-17 structures was superimposed in seven-residue stretches, and the root-mean-square deviation (rmsd) of backbone atoms was calculated (Figure 4C). (At superposition lengths of eight residues or greater, no RMSDs below 0.88 ± 0.2 Å were observed.) For a seven-residue superposition, the backbone atom rmsd is the lowest over R6−K12, suggesting that this region is well converged and mirroring the observation of highly defined ϕ and ψ dihedral angles. RMSDs over seven residues indicate that both the N- and C-terminal regions of apelin-17 are relatively unstructured in the presence of SDS micelles. Using Promotif-NMR,(38) 45 type I and 374 type IV β-turns were detected in the final ensemble (Table 2), with 98% of the type I β-turns being initiated between R6 and L9. Out of 80 structures, 30 have a type I β-turn initiation at P7. Type IV β-turns appear to be distributed throughout apelin-17, although there is a very well-defined type IV β-turn initiated at S10 in 77/80 of the ensemble members (Figure S2 in the Supporting Information). Paramagnetic relaxation enhancement experiments (Figure 3) indicate that the structural convergence over R6−K12 is the result of apelin binding to the micelle. In the superposed structural ensemble, the cationic side-chain atoms of R6 and R8 also tend to lie on the same face of the peptide, providing a cationic surface that may interact with the anionic micelle headgroups (Figure 5B). Since the structure of apelin-17 induced by anionic micelle binding is consistent between SDS and LPPG, as observed with CD spectropolarimetry, the NMR ensemble generated for apelin-17 interacting with SDS is also representative of the apelin-17 structure when bound to LPPG micelles.


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

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

Structure of apelin-17 bound to an SDS micelle: (A) superposition of all 80 members of the final ensemble of structures from R6 to K12 (R6−K12 colored blue, remainder green) with P7 and S10, initiation points of type I and type IV β-turns, respectively, indicated; (B) zoom of the superposition in (A) (backbone atoms green) showing cationic side chains of R6 and R8 (blue; all other side chains red) falling on the same face of apelin-17; (C) superposition of all heavy atoms of M15−F17 for all 80 ensemble members, with the backbone shown in blue and side chains colored red.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: Structure of apelin-17 bound to an SDS micelle: (A) superposition of all 80 members of the final ensemble of structures from R6 to K12 (R6−K12 colored blue, remainder green) with P7 and S10, initiation points of type I and type IV β-turns, respectively, indicated; (B) zoom of the superposition in (A) (backbone atoms green) showing cationic side chains of R6 and R8 (blue; all other side chains red) falling on the same face of apelin-17; (C) superposition of all heavy atoms of M15−F17 for all 80 ensemble members, with the backbone shown in blue and side chains colored red.
Mentions: Independent of this, the ensemble of apelin-17 structures was superimposed in seven-residue stretches, and the root-mean-square deviation (rmsd) of backbone atoms was calculated (Figure 4C). (At superposition lengths of eight residues or greater, no RMSDs below 0.88 ± 0.2 Å were observed.) For a seven-residue superposition, the backbone atom rmsd is the lowest over R6−K12, suggesting that this region is well converged and mirroring the observation of highly defined ϕ and ψ dihedral angles. RMSDs over seven residues indicate that both the N- and C-terminal regions of apelin-17 are relatively unstructured in the presence of SDS micelles. Using Promotif-NMR,(38) 45 type I and 374 type IV β-turns were detected in the final ensemble (Table 2), with 98% of the type I β-turns being initiated between R6 and L9. Out of 80 structures, 30 have a type I β-turn initiation at P7. Type IV β-turns appear to be distributed throughout apelin-17, although there is a very well-defined type IV β-turn initiated at S10 in 77/80 of the ensemble members (Figure S2 in the Supporting Information). Paramagnetic relaxation enhancement experiments (Figure 3) indicate that the structural convergence over R6−K12 is the result of apelin binding to the micelle. In the superposed structural ensemble, the cationic side-chain atoms of R6 and R8 also tend to lie on the same face of the peptide, providing a cationic surface that may interact with the anionic micelle headgroups (Figure 5B). Since the structure of apelin-17 induced by anionic micelle binding is consistent between SDS and LPPG, as observed with CD spectropolarimetry, the NMR ensemble generated for apelin-17 interacting with SDS is also representative of the apelin-17 structure when bound to LPPG micelles.

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