Biomedical subjects

Sarah R Dennison

Publications and source records attributed to Sarah R Dennison.

10 recordsLinked to original sources

PubMed2006

The interactions of aurein 1.2 with cancer cell membranes.

Here, the interactions of aurein 1.2, a defence peptide, with T98G glioblastoma cell membranes are studied. The peptide induced maximal surface pressure changes of circa 9 mN m(-1) in monolayers of endogenous T98G membrane lipid. Reducing monolayer anionic lipid showed a positive correlation (R(2)>0.91) with decreases in maximal surface pressure changes induced by aurein 1.2 (circa 3 mN m(-1) in the absence of this lipid). Cancer cell membrane invasion by the peptide therefore appears not to be mediated by lipid receptors or specific lipid requirements but rather a general requirement for anionic lipid and/or other negatively charged membrane components.

Antimicrobial Cationic Peptides↗

PubMed2006

Interactions of an anionic antimicrobial peptide with Staphylococcus aureus membranes.

The antimicrobial activity of the anionic peptide, AP1 (GEQGALAQFGEWL), was investigated. AP1 was found to kill Staphylococcus aureus with an MLC of 3mM and to induce maximal surface pressure changes of 3.8 mN m(-1) over 1200s in monolayers formed from lipid extract of S. aureus membranes. FTIR spectroscopy showed the peptide to be alpha-helical (100%) in the presence of vesicles formed from this lipid extract and to induce increases in their fluidity (Deltanu circa 0.5 cm(-1)). These combined data show that AP1 is able to function as an alpha-helical antimicrobial peptide against Gram-positive bacteria and suggest that the killing mechanism used by the peptide involves interactions with the membrane lipid headgroup region. Moreover, this killing mechanism differs strongly from that previously reported for AP1 against Gram-negative bacteria, indicating the importance of considering the effects of membrane lipid composition when investigating the structure/function relationships of antimicrobial peptides.

Anti-Bacterial Agents↗

PubMed2006

Investigations into the ability of an oblique alpha-helical template to provide the basis for design of an antimicrobial anionic amphiphilic peptide.

AP1 (GEQGALAQFGEWL) was shown by theoretical analysis to be an anionic oblique-orientated alpha-helix former. The peptide exhibited a monolayer surface area of 1.42 nm(2), implying possession of alpha-helical structure at an air/water interface, and Fourier transform infrared spectroscopy (FTIR) showed the peptide to be alpha-helical (100%) in the presence of vesicle mimics of Escherichia coli membranes. FTIR lipid-phase transition analysis showed the peptide to induce large decreases in the fluidity of these E. coli membrane mimics, and Langmuir-Blodgett trough analysis found the peptide to induce large surface pressure changes in monolayer mimics of E. coli membranes (4.6 mN.m(-1)). Analysis of compression isotherms based on mixing enthalpy (DeltaH) and the Gibbs free energy of mixing (DeltaG(Mix)) predicted that these monolayers were thermodynamically stable (DeltaH and DeltaG(Mix) each negative) but were destabilized by the presence of the peptide (DeltaH and DeltaG(Mix) each positive). The peptide was found to have a minimum lethal concentration of 3 mm against E. coli and was seen to cause lysis of erythrocytes at 5 mm. In combination, these data clearly show that AP1 functions as an anionic alpha-helical antimicrobial peptide and suggest that both its tilted peptide characteristics and the composition of its target membrane are important determinants of its efficacy of action.

Amino Acid Sequence↗

PubMed2006

Oblique orientated alpha-helices and their prediction.

Oblique orientated alpha-helices possess hydrophobicity gradients, which allow the parent alpha-helices to penetrate the membrane at a shallow angle, thereby destabilising membrane lipid organisation and promoting a range of biological processes. These alpha-helices occur in a variety of membrane interactive proteins and a number of techniques have been developed to guide their identification using sequence data alone. Hydrophobicity profiling, which provides a one-dimensional analysis of sequence data, identified only 30% of known tilted peptides in a control dataset and was thus of limited predictive use. In contrast, extended hydrophobic moment plot methodology and amphipilic profiling which take residue distribution into account and provide two-dimensional analysis of primary structural data, were found to be good indicators of tilted peptide structure. Amphiphilic profiling identified 67% of tilted peptides in the control dataset and showed that potentially, approximately 40% of transmembrane alpha-helices possess tilted peptide structure. However, it has been shown that extending these simple methods to take into account the three-dimensional spatial distribution of residues gives no clear additional benefit to identifying tilted peptides.

Amino Acid Sequence↗

PubMed2006

Anticancer alpha-helical peptides and structure/function relationships underpinning their interactions with tumour cell membranes.

Cancer is a major cause of premature death and there is an urgent need for new anticancer agents with novel mechanisms of action. Here we review recent studies on a group of peptides that show much promise in this regard, exemplified by arthropod cecropins and amphibian magainins and aureins. These molecules are alpha-helical defence peptides, which show potent anticancer activity (alpha-ACPs) in addition to their established roles as antimicrobial factors and modulators of innate immune systems. Generally, alpha-ACPs exhibit selectivity for cancer and microbial cells primarily due to their elevated levels of negative membrane surface charge as compared to non-cancerous eukaryotic cells. The anticancer activity of alpha-ACPs normally occurs at micromolar levels but is not accompanied by significant levels of haemolysis or toxicity to other mammalian cells. Structure/function studies have established that architectural features of alpha-ACPs such as amphiphilicty levels and hydrophobic arc size are of major importance to the ability of these peptides to invade cancer cell membranes. In the vast majority of cases the mechanisms underlying such killing involves disruption of mitochondrial membrane integrity and/or that of the plasma membrane of the target tumour cells. Moreover, these mechanisms do not appear to proceed via receptor-mediated routes but are thought to be effected in most cases by the carpet/toroidal pore model and variants. Usually, these membrane interactions lead to loss of membrane integrity and cell death utilising apoptic and necrotic pathways. It is concluded that that alpha-ACPs are major contenders in the search for new anticancer drugs, underlined by the fact that a number of these peptides have been patented in this capacity.

Amino Acid Sequence↗

PubMed2005

Deuteration can affect the conformational behaviour of amphiphilic alpha-helical structures.

The replacement of hydrogen with deuterium is frequently used in conjunction with neutron diffraction to investigate peptide-membrane interaction. This isotopic substitution in an amino acid residue radically changes the neutron scatter pattern of the peptide, thereby allowing its localisation within the bilayer with the aid of derived Fourier maps. Nonetheless, this technique relies on the generally held assumption that normal and isotopically enriched protein species do not differ significantly in structure or biological activity. Recently, this assumption has been questioned and here, diffraction data from studies on a membrane interactive peptide clearly challenge the reliability of this assumption.

Chemical Phenomena↗

PubMed2005

Investigations into the membrane interactions of m-calpain domain V.

m-calpain is a calcium-dependent heterodimeric protease implicated in a number of pathological conditions. The activation of m-calpain appears to be modulated by membrane interaction, which has been predicted to involve oblique-orientated alpha-helix formation by a GTAMRILGGVI segment located in domain V of the protein's small subunit. Here, we have investigated this prediction. Fourier transform infrared conformational analysis showed that VP1, a peptide homolog of this segment, exhibited alpha-helicity of approximately 45% in the presence of dimyristoylphosphatidylcholine/dimyristoylphosphatidylserine (DMPS) vesicles. The level of helicity was unaffected over a 1- to 8-mM concentration range and did not alter when the anionic lipid composition of these vesicles was varied between 1% and 10% DMPS. Similar levels of alpha-helicity were observed in trifluoroethanol and the peptide appeared to adopt alpha-helical structure at an air/water interface with a molecular area of 164 A(2) at the monolayer collapse pressure. VP1 was found to penetrate dimyristoylphosphatidylcholine/DMPS monolayers, and at an initial surface pressure of 30 mN m(-1), the peptide induced surface pressure changes in these monolayers that correlated strongly with their anionic lipid content (maximal at 4 mN m(-1) in the presence of 10% DMPS). Neutron diffraction studies showed VP1 to be localized at the hydrophobic core of model palmitoyloleylphosphatidylcholine/palmitoyloleylphosphatidylserine (10:1 molar ratio) bilayer structures and, in combination, these results are consistent with the oblique membrane penetration predicted for the peptide. It would also appear that although not needed for structural stabilization anionic lipid was required for membrane penetration.

Calpain↗

PubMed2005

Are oblique orientated alpha-helices used by antimicrobial peptides for membrane invasion?

Oblique orientated alpha-helices are highly specialised protein structural elements that penetrate membranes at a shallow angle and are used to promote membrane destabilisation by a number of protein classes. Here, the use of extended hydrophobic moment methodology shows that the amphibian extrudates, aurein 1.2 and citropin 1.1, may use oblique orientated alpha-helices in their antimicrobial action and that such use may be shared by other antimicrobial peptides. This appears to be the first systematic analysis of these peptides for the possession of oblique orientated alpha-helical structure.

Amino Acid Sequence↗

PubMed2005

Amphiphilic alpha-helical antimicrobial peptides and their structure/function relationships.

To facilitate microbial membrane invasion, amphiphilic alpha-helical antimicrobial peptides (alpha-AMPs) show a spatial segregation of hydrophobic and hydrophilic residues about the alpha-helical long axis. Here we discuss potential mechanisms by which these peptides are able to disrupt membrane structure and the structural characteristics, which are required for function.

Amino Acids↗

PubMed2003

Factors determining the efficacy of alpha-helical antimicrobial peptides.

A database of alpha-helical antimicrobial peptides (AMP) was established and their minimum inhibitory concentrations (MIC) were compared with their physiochemical characteristics in an attempt to establish those features that determine efficacy. There is no significant difference in AMP sensitivity between Gram-positive and Gram-negative bacteria but fungi did require higher concentrations to achieve the same degree of growth inhibition. For antibacterial peptides there appears to be a positive correlation between MIC and hydrophobic arc size and a negative correlation between MIC and net charge.

Animals↗