Calcium‐binding properties and molecular organization of bradykinin

Abstract

The NMR features of bradykinin were investigated in dimethylsulfoxide containing 1% water. The temperature dependence of chemical shifts and ROESY maps were monitored for the major species where all X±Pro bonds are trans. The occurrence of a head-to-tail ionic interaction and intramolecular hydrogen bonds stabilizing a pseudo cyclic arrangement was inferred, a b turn at the C-terminus being the main feature of the secondary structure. Calcium was shown to bind to the peptide with a dissociation constant K d = 2.8 + 0.2 mm.2 Pro and 3 Pro carbonyls, as well as the 9 Arg carboxyl, were assigned as the metal-binding sites. A molecular model of the 1 : 1 metal± complex was obtained. In light of conformational changes experienced by the peptide upon interaction with calcium, a role for the metal was hypothesized in the process of conformational selection from the free to the receptor-bound state of bradykinin.Keywords: bradykinin; calcium; conformational selection; NMR.The activity of the two main kinin peptides (bradykinin, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Ser, and kallidin, Lys-bradykinin), is mediated by a G-protein-coupled receptor (B2) expressed in nearly all cells. Receptor activation causes a cascade of events [1]; kinins have therefore been implicated as relevant mediators in several pathophysiologies, including the peripheral inflammatory processes associated with Alzheimer's disease [2].Links between calcium homeostasis and/or signalling and the stimulation of kinin receptors in mammalian cells have been well established by an enormous body of literature, especially in recent years (e.g. Refs 3±5). However, to our knowledge, the direct effect of calcium upon the conformational equilibria of kinin peptides in solution has not been investigated so far, in spite of the attainable beneficial information.The presence of three prolines in the sequence is expected to yield structural heterogeneity in solution, because the cis-trans interconversion at each X±Pro bond may provide up to eight stable isomers, depending on environmental parameters. Several CD and NMR investigations in a number of solvent systems have occasionally detected transient ordered structures, similar to g turns and b turns [6±23]; however, the net result of a random coil peptide was obtained in all cases due to the fast rate of exchange between the extended structures. Such a high degree of flexibility suggests that binding to the receptor implies the selection of a particular structure from among the number of slowly or rapidly interconverting ones in solution. As a matter of fact, enhancement of the b-turn-forming potential of bradykinin was observed in the presence of SDS micelles [16,24±27], apolar organic solvents [14,18,20,27] or aqueous phospholipids [13,22,26]; as a consequence of all these findings, bradykinin is currently believed to adopt a C-terminal b turn upon complexation with the receptor [28].In the present study, NMR data were collected for bradykinin in dimethylsulfoxide containing 1% water in the presence of calcium, in orde...

Conformational basis for the biological activity of TOAC‐labeled angiotensin II and bradykinin: Electron paramagnetic resonance, circular dichroism, and fluorescence studies

“…Similar to AII, the conformation of BK in aqueous solution is considered to consist of an equilibrium between interconverting states, resulting from the peptide flexibility 67–70 . 13 C and 1 H NMR studies indicated that the trans configuration about the X‐Pro peptide bond is strongly favored 67.…”

A Canonical EF‐Loop Directs Ca2+‐Sensitivity in Phospholipase C‐η2

“…The dipolar aprotic solvent DMSO-d 6 was chosen because signals for labile protons such as those of the NH backbone protons, are often reduced or missing in aqueous media due to exchange with bulk water but readily observed in DMSO. Most peptides have good solubility in DMSO, and a large number of conformational studies of short peptides have been carried out in DMSO-d 6 (Oliva et al, 2000), including studies on Ca-binding peptides (Gaggelli et al, 1999). It is noteworthy that DMSO does not induce secondary structure (Yeagle et al, 2007), can act as an H-bond acceptor, but not a donor, and has a weaker tendency than water to co-ordinate to metal ions.…”

Interaction and structural study of kinin peptide bradykinin and ganglioside monosialylated 1 micelle

“…2,3 It plays many roles in pathophysiology, particularly as an initiator of inflammation. 4,5 This peptide exerts biological effects by binding to specific G-protein-coupled receptors 6 (B2) on the cell membrane, thereby triggering a series of poorly understood biochemical events that are manifested by pain, 7 contraction of smooth muscle, lowering of arterial pressure, 8 etc. Interactions of bradykinin with natural as well as artificial membranes are extensively investigated in order to elucidate the mechanism of the physiological activity of the peptide by several spectroscopic studies including CD, 9-11 13 C-and 1 H-NMR, [10][11][12] laser Raman spectroscopy, 13 and electron spin resonance spectroscopy, 14,15 The results suggested that the peptide's biological activity could be correlated with the extent of its interaction with the vesicles, supporting the hypothesis of an active role of the membrane as a catalyst for peptide-receptor interaction.…”