Structure and Mode-of-Action of the Two-Peptide (Class-IIb) Bacteriocins

This review focuses on the structure and mode-of-action of the two-peptide (class-IIb) bacteriocins that consist of two different peptides whose genes are next to each other in the same operon. Optimal antibacterial activity requires the presence of both peptides in about equal amounts. The two peptides are synthesized as preforms that contain a 15–30 residue double-glycine-type N-terminal leader sequence that is cleaved off at the C-terminal side of two glycine residues by a dedicated ABC-transporter that concomitantly transfers the bacteriocin peptides across cell membranes. Two-peptide bacteriocins render the membrane of sensitive bacteria permeable to a selected group of ions, indicating that the bacteriocins form or induce the formation of pores that display specificity with respect to the transport of molecules. Based on structure–function studies, it has been proposed that the two peptides of two-peptide bacteriocins form a membrane-penetrating helix–helix structure involving helix–helix-interacting GxxxG-motifs that are present in all characterized two-peptide bacteriocins. It has also been suggested that the membrane-penetrating helix–helix structure interacts with an integrated membrane protein, thereby triggering a conformational alteration in the protein, which in turn causes membrane-leakage. This proposed mode-of-action is similar to the mode-of-action of the pediocin-like (class-IIa) bacteriocins and lactococcin A (a class-IId bacteriocin), which bind to a membrane-embedded part of the mannose phosphotransferase permease in a manner that causes membrane-leakage and cell death

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

The Three-Dimensional NMR-Structure of the Membrane-Permeabilizing Pediocin-Like Antimicrobial Peptide Curvacin A in Lipid Micelles

Antimicrobial peptides produced by lactic acid bacteria (LAB) are extensively studied, but little is know about their three-dimensional structures. Solution structures of these peptides will be useful to gain information about their mode of action, which again is important for further use of these substances in industry and medicine. Curvacin A is an antimicrobial peptide that belongs to the family of pediocin-like bacteriocins. Curvacin A was produced from its natural LAB producer, Lactobacillus curvatus LTH1174, and purified by ion-exchange- and reverse phase chromatography. Circular Dichroism-experiments revealed that curvacin A was unstructured in water, but became structured upon interactions with membrane-mimicking environments such as dodecyl phosphocholin (DPC)-micelles. The three-dimensional structure of curvacin A in DPC-micelles has been elucidated by the use of nuclear magnetic resonance (NMR)-spectroscopy. Curvacin A was shown to contain three regions: an N-terminal S-shaped ƒÒ-sheet like domain (residues 2-15), a central polar helix (residues 19-24) and an amphiphilic C-terminal helix (residues 29-39). The C-terminal tail consists of only two residues (G40 and M41) and seems to be unstructured. There was a hinge between the three regions, enabling the regions to move relative to each other