Inactivating Peptide Of The Shaker B K+ Channel

TABLE 1 Fluorescence emission maxima (λmax) and surface partitioning constants (Kp*) exhibited by NBD-labeled peptides in the presence of phospholipid vesicles

| λmax (nm) | | | | | Kp* x 10-4 (M-1) | |
Peptidedesignation | pH | Buffer | PC | PA | PG | | PC | PA | PG |
| || | | | | | | |
ShB-NBD | 7 | 555 | 551 | 531 | 534 | | No binding | 77.1 (±11.6) | 2.80 (±1.10) |ShBL7E-NBD | 7 | 554 | 551 | 533 | 534 | | No binding | 3.05 (±1.45) | 0.72 (±0.20) |
ShB-NBD | 8.5 | 552 | - | 530 | 536 | |- | 1.95 (±0.65) | 0.64 (±0.09) |
ShBL7E-NBD | 8.5 | 553 | - | 536 | 552 | | - | 0.65 (±0.025) | ≥0.05 |as large as that produced by the ShB peptide (pKa ~7.7), which seems consistent with the experiments using fluorescently labeled peptides in which the surface partition coefficients estimated for the interaction of the ShB peptide with PA vesicles were always higher than those corresponding to the ShB-L7E peptide.

Differential scanning calorimetricstudies of peptide insertion into lipid bilayers


The possible implication of the hydrophobic domains of the phospholipid bilayers in the association of the peptides with the vesicles was investigated by DSC using synthetic dimirystoyl derivatives of the different phospholipids, which have convenient phase transition temperatures at 23.5ºC, 23.3ºC and49.6ºC, for DMPC, DMPG and DMPA, respectively. In these experiments, peptide insertion into the lipid bilayer and therefore, its interaction with the phospholipid acyl chains are expected to prevent part of the phospholipid molecules from undergoing the phase transition characteristic of the "pure" phospholipid species and thus decrease the phase transition enthalpy in a peptide concentration-dependent manner (Papahadjopoulos et al., 1975). We observed that neither the ShB nor the ShB-L7E peptides cause any effects on the transition temperature or the transition enthalpy of DMPC vesicles (data not shown). On the other hand, confronting the ShB peptide to anionic phospholipid vesicles (Fig. 2, A and B) causes a large, concentration-dependent decrease in the transition enthalpy, which isslightly more pronounced in DMPG than in DMPA vesicles, without modifying the phase transition temperature. A plot of the observed changes in the transition enthalpies versus the peptide/phospholipid molar ratios used in these studies (Fig. 2 C), predicts that each ShB peptide molecule prevents an average of three to four anionic phospholipid molecules from undergoing the phase transition. As for...