Stabilization of an isolated helical capping box in solution by hydrophobic interactions: evidence from the NMR study of bioactive peptides from the C-terminus of human C5a anaphylatoxin

Residues 10-18 within the C5a receptor N terminus compose a binding domain for chemotaxis inhibitory protein of Staphylococcus aureus

Chemotaxis inhibitory protein of Staphylococcus aureus (CHIPS) is excreted by the majority of S. aureus strains and is a potent inhibitor of C5a- and formylated peptide-mediated chemotaxis of neutrophils and monocytes. Recently, we reported that CHIPS binds to the C5a receptor (C5aR) and the formylated peptide receptor, thereby blocking activation by C5a and formylated peptides, respectively. The anaphylatoxin C5a plays an important role in host immunity and pathological inflammatory processes. For C5a a two-site binding model is proposed in which C5a initially binds the C5aR N terminus, followed by interaction of the C5a C-terminal tail with an effector domain on the receptor. We have shown here that CHIPS does not affect activation of the C5aR by a peptide mimic of the C5a C terminus. Moreover, CHIPS was found to bind human embryonic kidney 293 cells expressing only the C5aR N terminus. Deletion and mutation experiments within this C5aR N-terminal expression system revealed that the binding site of CHIPS is contained in a short stretch of 9 amino acids (amino acids 10-18), of which the aspartic acid residues at positions 10, 15, and 18 plus the glycine at position 12 are crucial. Binding studies with C5aR/C3aR and C5aR/IL8RA chimeras confirmed that CHIPS binds only to the C5aR N terminus without involvement of its extracellular loops. CHIPS may provide new strategies to block the C5aR, which may lead to the development of new C5aR antagonists.

Structure-function relationships of human C5a and C5aR

Using peptides that represent linear regions of the powerful complement activation product, C5a, or loops that connect the four alpha helices of C5a, we have defined the ability of these peptides to reduce binding of (125)I-C5a to human neutrophils, inhibit chemotactic responses of neutrophils to C5a, and reduce H(2)O(2) production in neutrophils stimulated with PMA. The data have defined likely sites of interaction of C5a with C5aR. The peptides had no functional activity per se on neutrophils and did not interfere with neutrophil responses to the unrelated chemotactic peptide, N-formyl-Met-Leu-Phe. Although previous data have suggested that there are two separate sites on C5a reactive with C5aR, the current data suggest that C5a interacts with C5aR in a manner that engages three discontinuous regions of C5a.

Determination of structural elements related to the biological activities of a potent decapeptide agonist of human C5a anaphylatoxin

The structural features related to the biologic activities of a potent, response-selective decapeptide agonist of human C5a, YSFKPMPLaR (C5a65-74, Y65, F67, P69, P71, D-Ala73), were identified by NMR analysis in H2O, DMSO and TFE. This investigation showed that the KPM residues in H2O and the SFKPM residues in DMSO exhibited an extended backbone conformation, whereas a twisted conformation was found in this region in TFE. In H2O, the C-terminal region (PLaR) adopted a distorted type II beta-turn or a type II/V beta-turn. In the type IIN beta-turn, Leu72 exhibited a conformation typical of a type II beta-turn, whereas D-Ala73 exhibited a conformation characteristic of a type V beta-turn. Furthermore, a gamma-turn involving residues LaR overlapped with the type II/V beta-turn. In DMSO, the C-terminal region had the analogous turn-like motif (type II/V beta-turn overlapping with gamma-turn) found in H2O. In TFE, no beta-turn motifs were formed by the PLaR residues. These turn-like motifs in the C-terminal region of the peptide in both H2O and DMSO were in agreement with the biologically important conformations predicted earlier by a structure-function analysis of a related panel of decapeptide analogs. The motifs determined by the NMR analysis of YSFKPMPLaR in H2O and DMSO may represent structural elements important for C5a agonist activity and thus can be used to design the next generation of C5a agonist, partial agonist and antagonist analogs.

Characterization of flexible molecules in solution: the RGDW peptide

Molecular dynamics simulations with adaptive umbrella sampling of the potential energy are used to study conformations of the adhesion peptide RGDW. The peptide is simulated in a box of explicit water. It results in a combination of room temperature (300 K) simulations, in which conformations dominating the average properties of the system are sampled, with high temperature ( approximately 1000 K) simulations in which free energy barriers separating different local minima are crossed efficiently. The simulations with explicit water are compared to simulations of the isolated peptide using different treatments of the electrostatics, and to published experimental data. There is good agreement for data related to the backbone conformation of the peptide. Some discrepancies are evident for data related to side-chain conformations. Together the simulations and experiments provide a description of the RGDW system that is more detailed and reliable than what can be obtained by either simulations or experiments alone.

NMR analysis of a potent decapeptide agonist of human C5a anaphylatoxin

A NMR investigation in H2O, TFE and DMSO of a conformationally constrained, potent decapeptide agonist of human C5a, YSFKDMPLaR (C5a65-74, Y65, F67, P71, D-Ala73) showed that its N-terminal region (YSFKD) exhibited an extended backbone conformation in H2O and a more twisted conformation in both TFE/H2O (30:70, v/v; referred to as TFE) and DMSO. The C-terminal region (MPLaR) of the peptide adopted compact, turn-like structures. In H2O, the C-terminal region adopted a type II beta-turn or a distorted type V/II beta-turn involving residues PLaR. In the distorted type V/II beta-turn, Leu72 exhibited a conformation typical of a type V beta-turn, whereas D-Ala73 exhibited a conformation typical of a type II beta-turn. The distorted type V/II beta-turn overlapped with an inverse gamma-turn involving residues MPL. In DMSO, the C-terminal region had the analogous inverse gamma-turn and the V/II beta-turn found in H2O. In many of the DMSO structures, two inverse gamma-turns in the MPL and PLa positions formed a double-inverse gamma-turn. None of the turns observed in H2O were present in TFE. However, in TFE, the PLa residues formed an inverse gamma-turn. Overall, the turn-like structural motifs in the C-terminal region of the peptide in both H2O and DMSO (but not in TFE) agreed with the biologically important conformations obtained earlier by the structure-function analysis of a panel of C5a agonist peptides. These motifs may represent key structural elements important for C5a agonist activity and may be used to design the next generation of C5a agonist and antagonist analogues.

Comparison of the solution conformations of a human immunodeficiency virus peptidomimetic and its retro-inverso isomer using 1H NMR spectroscopy

The solution conformations of the all L-alpha-peptide 1 and the corresponding retro-all D-alpha-peptide 2, two 20-metric peptides which generate antibodies that cross-react with the gp 120 envelop protein of human immunodeficiency virus-1 (HIV-1), have been investigated by high-field 1H NMR spectroscopy. Complete sequential and inter-residue interaction assignments were made from the 2D NMR spectra acquired at 500 MHz and 600 MHz in 40% deuterotrifluoroethanol (d3-TFE)/H2O at pH 2.3, and in 300 mM sodium dodecyl sulphate (SDS) in 100% D2O or 90% H2O/10% D2O at pH 2.6. Based on analysis of the nuclear Overhauser effect (NOE) and amide exchange data, peptide 1 and its retro-inverso isomer 2 in the polar solvent environment of 40% d3-TFE/H2O at pH 2.3 show very similar topological features. However, in the relatively non-polar 300 mM SDS micellar environment, peptides 1 and 2 exhibit differences in their solution structures in terms of the amide backbone and side-chain orientations. In particular, under the SDS micellar condition, peptide 1 maintains much of the secondary structure observed for this 20-mer peptide in 40% d3-TFE/H2O, pH 2.3, whereas peptide 2 adopts a more extended structure. These NMR results provide the first confirmation that the secondary structure of the all L-a-peptide 1 is maintained in both polar and non-polar environments, whereas the secondary structure and topology of the notionally equivalent retro-inverso isomer depends more on the solvent conditions. These results with the all L-a-peptide 1 and its retro-inverso isomer 2 provide important insight into the conformational influences of the C- and N-end group with L-alpha- and retro-D-alpha-isomer pairs in non-polar environments, and thus have general relevance to the design of bioactive retro-inverso peptidomimetic analogues related to immunogenic or hormonal peptides.