Helix fraying and lipid-dependent structure of a short amphipathic membrane-bound peptide revealed by solid-state NMR

The amphipathic a-helical peptide KIA14 [(KIAGKIA)(2)-NH2] was studied in membranes using circular dichroism and solid-state NMR spectroscopy to obtain global as well as local structural information. By analyzing H-2 NMR data from 10 analogues of KIA14 that were selectively labeled with Ala-d(3), those positions that are properly folded into a helix could be determined within the membrane-bound peptide. The N-terminus was found to be unraveled, whereas positions 4-14 formed an ideal helix all the way to the C-terminus. The helicity did not change when Gly residues were replaced by Ala-d3 but was reduced when Ile was replaced, indicating that large hydrophobic residues are required for membrane binding and helix formation. The reduced helicity was strongly correlated with a decrease in peptide-induced leakage from lipid vesicles. The orientation of the short KIA14 peptide was assessed in several lipid systems and compared with that of the longer KIA21 sequence [(KIAGKIA)(3)-NH2]. In 1,2-dioleoylsn-glycero-3-phosphatidylcholine, both peptides are aligned flat on the membrane surface, whereas in 1,2-dimyristoyl-sn-glycero3-phosphatidylcholine (DMPC)/1-myristoy1-2-hydroxy-sn-glycero-3-phosphatidylcholine (lyso-MPC) both are inserted into the membrane in an upright orientation. These two types of lipid systems had been selected for their strongly negative and positive spontaneous curvature, respectively. We propose that in these cases, the peptide orientation is largely determined by the lipid properties. On the other hand, in plain DMPC and 1,2-dilauroyl-sn-glycero-3-phosphatidylcholine, which have only a slight positive curvature, a marked difference in orientation is evident: the short KIA14 lies almost flat on the membrane surface, whereas the longer KIA21 is more tilted. We thus propose that out of the lipid systems tested here, DMPC (with hardly any curvature) is the least biased,lipid system in which peptide orientation and realignment can be studied, allowing to compare and discriminate the intrinsic effects of the properties of the peptides as such

Mode of action of antimicrobial peptides: long and short amphipathic alpha-helixes use different mechanisms

1 pag. -- 58th Annual Meeting of the Biophysical-Societ

Influence of the length and charge on the activity of alpha-helical amphipathic antimicrobial peptides

Hydrophobic mismatch is important for pore forming amphipathic antimicrobial peptides, as demonstrated recently [Grau-Campistany, A., et al. (2015) Sci. Rep. 5, 9388]. A series of different length peptides have been generated with the heptameric repeat sequence KIAGKIA, called KIA peptides, and it was found that only those helices sufficiently long to span the hydrophobic thickness of the membrane could induce leakage in lipid vesicles; there was also a clear length dependence of the antimicrobial and hemolytic activities. For the original KIA sequences, the cationic charge increased with peptide length. The goal of this work is to examine whether the charge also has an effect on activity; hence, we constructed two further series of peptides with a sequence similar to those of the KIA peptides, but with a constant charge of +7 for all lengths from 14 to 28 amino acids. For both of these new series, a clear length dependence similar to that of KIA peptides was observed, indicating that charge has only a minor influence. Both series also showed a distinct threshold length for peptides to be active, which correlates directly with the thickness of the membrane. Among the longer peptides, the new series showed activities only slightly lower than those of the original KIA peptides of the same length that had a higher charge. Shorter peptides, in which Gly was replaced with Lys, showed activities similar to those of KIA peptides of the same length, but peptides in which Ile was replaced with Lys lost their helicity and were less active