Throughout the biological world, a 30 A hydrophobic film typically delimits the environments that serve as the margin between life and death for individual cells. Biochemical and biophysical findings have provided a detailed model of the composition and structure of membranes, which includes levels of dynamic organization both across the lipid bilayer (lipid asymmetry) and in the lateral dimension (lipid domains) of membranes. How do cells apply anabolic and catabolic enzymes, translocases and transporters, plus the intrinsic physical phase behaviour of lipids and their interactions with membrane proteins, to create the unique compositions and multiple functionalities of their individual membranes?

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Membrane lipids: where they are and how they behave.

Antimicrobial peptides are an abundant and diverse group of molecules that are produced by many tissues and cell types in a variety of invertebrate, plant and animal species. Their amino acid composition, amphipathicity, cationic charge and size allow them to attach to and insert into membrane bilayers to form pores by 'barrel-stave', 'carpet' or 'toroidal-pore' mechanisms. Although these models are helpful for defining mechanisms of antimicrobial peptide activity, their relevance to how peptides damage and kill microorganisms still need to be clarified. Recently, there has been speculation that transmembrane pore formation is not the only mechanism of microbial killing. In fact several observations suggest that translocated peptides can alter cytoplasmic membrane septum formation, inhibit cell-wall synthesis, inhibit nucleic-acid synthesis, inhibit protein synthesis or inhibit enzymatic activity. In this review the different models of antimicrobial-peptide-induced pore formation and cell killing are presented.

Antimicrobial peptides: pore formers or metabolic inhibitors in bacteria?

T e purpose of this review is to assess the nature and magnitudes of the dominant forces in protein folding. Since proteins are only marginally stable at room temperature,’ no type of molecular interaction is unimportant, and even small interactions can contribute significantly (positively or negatively) to stability (Alber, 1989a,b; Matthews, 1987a,b). However, the present review aims to identify only the largest forces that lead to the structural features of globular proteins: their extraordinary compactness, their core of nonpolar residues, and their considerable amounts of internal architecture. This review explores contributions to the free energy of folding arising from electrostatics (classical charge repulsions and ion pairing), hydrogen-bonding and van der Waals interactions, intrinsic propensities, and hydrophobic interactions. An earlier review by Kauzmann (1959) introduced the importance of hydrophobic interactions. His insights were particularly remarkable considering that he did not have the benefit of known protein structures, model studies, high-resolution calorimetry, mutational methods, or force-field or statistical mechanical results. The present review aims to provide a reassessment of the factors important for folding in light of current knowledge. Also considered here are the opposing forces, conformational entropy and electrostatics. The process of protein folding has been known for about 60 years. In 1902, Emil Fischer and Franz Hofmeister independently concluded that proteins were chains of covalently linked amino acids (Haschemeyer & Haschemeyer, 1973) but deeper understanding of protein structure and conformational change was hindered because of the difficulty in finding conditions for solubilization. Chick and Martin (191 1) were the first to discover the process of denaturation and to distinguish it from the process of aggregation. By 1925, the denaturation process was considered to be either hydrolysis of the peptide bond (Wu & Wu, 1925; Anson & Mirsky, 1925) or dehydration of the protein (Robertson, 1918). The view that protein denaturation was an unfolding process was

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Dominant forces in protein folding

Prediction of protein conformation.

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Principles Of Fluorescence Spectroscopy

The shape of the gel to liquid crystalline phase transition of dielaidoylphosphatidylethanolamine is markedly dependent on the method of sample preparation

Glucagon 1-6 has a maximum lipolytic activity (Lmax) in the rat adipocyte which is 66% of that of glucagon. The N epsilon-guanidyl derivative, modified at Lys12, has about the same Lmax as glucagon 1-6. Modifying the carboxyl groups of glucagon with glycinamide or removing the COOH-terminal residues with cyanogen bromide reduces Lmax to less than 25% of the level of glucagon. The potency of each of these analogs (A50) in microM is as follows: glucagon 6 X 10(-3); glucagon 1-6 2 X 10(-2); N epsilon-guanidyl glucagon 9 X 10(-3); glycinamide glucagon 10(-2); cyanogen bromide peptide of glucagon 2 X 10(-1). The ability of all of the glucagon analogs to stimulate adenyl cyclase was somewhat less than their lipolytic activities with the exception of the glycinamide derivative and the cyanogen bromide peptide, which were slightly more active in stimulating adenyl cyclase than in lipolysis. Glucagon 1-6 is much more potent in stimulating adipocyte than liver adenyl cyclase.

Lipolytic and adenyl-cyclase-stimulating activity of glucagon1–6: comparison with glucagon derivatives chemically modified in the 7–29 sequence

Barth syndrome (BTHS) is a rare inherited metabolic disease resulting from mutations in the gene of the enzyme tafazzin, which catalyzes the acyl chain remodeling of the mitochondrial-specific lipid cardiolipin (CL). Tissue samples of individuals with BTHS present abnormalities in the level and the molecular species of CL. In addition, in tissues of a tafazzin knockdown mouse as well as in cells derived from BTHS patients it has been shown that plasmalogens, a subclass of glycerophospholipids, also have abnormal levels. Likewise, administration of a plasmalogen precursor to cells derived from BTHS patients led to an increase in plasmalogen and to some extent CL levels. These results indicate an interplay between CL and plasmalogens in BTHS. This interdependence is supported by the concomitant loss in these lipids in different pathological conditions. However, currently the molecular mechanism linking CL and plasmalogens is not fully understood. Here, a review of the evidence showing the linkage between the levels of CL and plasmalogens is presented. In addition, putative mechanisms that might play a role in this interplay are proposed. Finally, the opportunity of therapeutic approaches based on the regulation of plasmalogens as new therapies for the treatment of BTHS is discussed.

Interplay between cardiolipin and plasmalogens in Barth syndrome.

(1999). Role of the Membrane in the Modulation of the Activity of Protein Kinase C. Journal of Liposome Research: Vol. 9, No. 1, pp. 21-41.

Richard M. Epand

Papers

The shape of the gel to liquid crystalline phase transition of dielaidoylphosphatidylethanolamine is markedly dependent on the method of sample preparation

Lipolytic and adenyl-cyclase-stimulating activity of glucagon1–6: comparison with glucagon derivatives chemically modified in the 7–29 sequence

Interplay between cardiolipin and plasmalogens in Barth syndrome.

Role of the Membrane in the Modulation of the Activity of Protein Kinase C

Preferential interaction of pentagastrin with the gel state of dimyristoyl glycerophosphocholine.