Proton NMR conformational study of an annexin I fragment: Influence of a phospholipidic micellar environment

Abstract

A 32 residue peptide, Ac-AQWDADELRAAMKGLGTDEDTLIELASRTNK, spanning the first helix-loop-helix motif of the second repeat of human annexin I, was synthesized and studied by standard 2D proton NMR and molecular modeling. The peptide was solubilized either in aqueous solution, in TFE-H2O mixtures or in aqueous phospholipidic micellar solution. In pure aqueous solution, elements of helix secondary structure were observed. Addition of TFE led to a dramatic cooperative effect on the secondary structure with a very low transition midpoint indicative of the strong tendency of the peptide to form alpha helices. Only in the aqueous micellar solution was the full helix-loop-helix motif obtained, showing again the potency of a membrane-like micellar environment to initiate peptide secondary structures and even elements of tertiary structure. There were sufficient NMR data to perform molecular modeling of the structure of the annexin fragment solubilized in the presence of micelles. However, this structure showed a relatively high degree of flexibility, especially around the T17-D18 hinge at the end of the loop.

Thermodynamic model of secondary structure for α-helical peptides and proteins

“…72 pair that can be present only at the C-terminus of the ahelix (as Ser 245 -Glu 246 of thermolysin, 2tmn), or imme-A similar hydrophobic interaction at the C-terminus of the a-helix between the bulky C and C4 or C1 side diately preceding a Pro-induced helix kink (as Ser 215 -Gln 216 in glucoamylase, 3gly, and Ser 21 -Gln 22 in cyto-chain when the C-cap residue is Gly, 73 the ''Schellman motif,'' is very common for proteins, 61,74 and has also chrome c, 2ccy). The total contribution of the interactions between the been found in crystal structures of a-helical peptides 75 and detected by nmr spectroscopy for peptides in the polar side chains was calculated assuming additivity of presence of SDS micelles [76][77][78][79] or trifluoroethanol. 71,80 The their pairwise DDG sch ij energies: Schellman motif is only marginally stable in water: no NOEs between the C and C1 or C4 side chains were DG sch…”

A high-resolution 1H NMR approach for structure determination of membrane peptides and proteins in non-deuterated detergent: Application to mastoparan X solubilized in n-octylglucoside

“…In particular, since the pioneering work of Brown and Wfithrich (Brown and WiJthrich, 1981;Brown et al, 1982), many studies have been performed on detergent-solubilized peptides and small proteins by ~H 2D NMR (for a review see Opella and McDonnell (1993)). This has led to the structure determination of several membrane peptides (Arseniev et al, 1985;Inagaki et al, 1989), small membrane proteins (Maurer and Riiterjans, 1994) and fragments of larger membrane proteins (Pervushin et al, 1991;Lomize et al, 1992;Macquaire et al, 1993). All these studies have invariably used deuterated detergent in order to fully observe the protein ~H resonances.…”

Protein Unfolding Transitions in an Intrinsically Unstable Annexin Domain: Molecular Dynamics Simulation and Comparison with Nuclear Magnetic Resonance Data

“…The A-helix has also an interesting feature in the simulation at the C terminus: the helix is longer than the native helix by two residues, G 17 L 18 which form a particular C-terminal motif with an additional A 14 -G 19 H-bond. This increase in helix length was experimentally observed as a i Ϫ (i Ϫ 4) NOE contact from L18 side-chain in the AB fragment (Macquaire et al, 1993). This structure leads to suppression of the AB loop.…”