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Objectives Here we report the draft genome sequence of Staphylococcus agnetis 4244, a strain involved in bovine mastitis, and its ability to inhibit different species of antibiotic-resistant Gram-positive bacteria owing to bacteriocin production. Methods An Illumina MiSeq platform was used for genome sequencing. De novo genome assembly was done using the A5-miseq pipeline. Genome annotation was performed by the RAST server, and mining of bacteriocinogenic gene clusters was done using the BAGEL4 and antiSMASH v.5.0 platforms. Investigation of the spectrum of activity of S. agnetis 4244 was performed on BHI agar by deferred antagonism assay. Results The total scaffold size was determined to be 2 511 708 bp featuring a G+C content of 35.6%. The genome contains 2431 protein-coding sequences and 80 RNA sequences. Genome analyses revealed three prophage sequences inserted in the genome as well as several genes involved in drug resistance and two bacteriocin gene clusters (encoding a thiopeptide and a sactipeptide) encoded on the bacterial chromosome. Staphylococcus agnetis 4244 was able to inhibit all 44 strains of antibiotic-resistant Gram-positive bacteria tested in this study, including vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA) and other antibiotic-resistant staphylococcal strains. Conclusion This study emphasises the potential biotechnological application of this strain for production of bacteriocins that could be used in the food industry as biopreservatives and/or in medicine as alternative therapeutic options against VRE, MRSA, vancomycin-intermediate S. aureus and other antibiotic-resistant Gram-positive bacteria, including biofilm-forming isolates. It also provides some genetic features of the draft genome of S. agnetis 4244.

The mammalian Na+/H+ exchanger isoform 1 (NHE1) is an integral membrane protein that regulates intracellular pH (pHi) by removing a single intracellular proton in exchange for one extracellular sodium ion. It is involved in cardiac hypertrophy and ischemia reperfusion damage to the heart and elevation of its activity is a trigger for breast cancer metastasis. NHE1 has an extensive 500 amino acid N-terminal membrane domain that mediates transport and consists of 12 transmembrane segments connected by intracellular and extracellular loops. Intracellular loops are hypothesized to modulate the sensitivity to pHi. In this study, we characterized the structure and function of intracellular loop 5 (IL5), specifically amino acids 431-443. Mutation of eleven residues to alanine caused partial or nearly complete inhibition of transport; notably, mutation of residues L432, T433, I436, N437, R440 and K443 demonstrated these residues had critical roles in NHE1 function independent of effects on targeting or expression. The nuclear magnetic resonance (NMR) solution spectra of the IL5 peptide in a membrane mimetic sodium dodecyl sulfate solution revealed that IL5 has a stable three-dimensional structure with substantial alpha helical character. NMR chemical shifts indicated that K438 was in close proximity with W434. Overall, our results show that IL5 is a critical, intracellular loop with a propensity to form an alpha helix, and many residues of this intracellular loop are critical to proton sensing and ion transport.

Bacteriocins are potent antimicrobial peptides that are ribosomally produced and exported by bacteria, presumably to aid elimination of competing microorganisms. Many circular and linear leaderless bacteriocins have a recuring three dimensional structural motif known as a saposin-like fold. Although these bacteriocin sizes and sequences are often quite different, and their mechanisms of action vary, this conserved motif of multiple helices appears critical for activity and may enable peptide–lipid and peptide–receptor interactions in target bacterial cell membranes. Comparisons between electrostatic surfaces and hydrophobic surface maps of different bacteriocins are discussed emphasizing similarities and differences in the context of proposed modes of action.

Lacticin Q (LnqQ) and aureocin A53 (AucA) are leaderless bacteriocins from Lactococcus lactis QU5 and Staphylococcus aureus A53, respectively. These bacteriocins are characterized by the absence of an N-terminal leader sequence and are active against a broad range of Gram-positive bacteria. LnqQ and AucA consist of 53 and 51 amino acids, respectively, and have 47% identical sequences. In this study, their three-dimensional structures were elucidated using solution nuclear magnetic resonance and were shown to consist of four α-helices that assume a very similar compact, globular overall fold (root-mean-square deviation of 1.7 Å) with a highly cationic surface and a hydrophobic core. The structures of LnqQ and AucA resemble the shorter two-component leaderless bacteriocins, enterocins 7A and 7B, despite having low levels of sequence identity. Homology modeling revealed that the observed structural motif may be shared among leaderless bacteriocins with broad-spectrum activity against Gram-positive organisms. The elucidated structures of LnqQ and AucA also exhibit some resemblance to circular bacteriocins. Despite their similar overall fold, inhibition studies showed that LnqQ and AucA have different antimicrobial potency against the Gram-positive strains tested, suggesting that sequence disparities play a crucial role in their mechanisms of action.

In this study, we report that CbnX (33 residues) and CbnY (29 residues) comprise a class IIb (two-component) bacteriocin in Carnobacteria. Individually, CbnX and CbnY are inactive, but together act synergistically to exert a narrow spectrum of activity. The structures of CbnX and CbnY in structure-inducing conditions were determined and strongly resemble other class IIb bacteriocins (i.e., LcnG, PlnEF, PlnJK). CbnX has an extended, amphipathic α-helix and a flexible C terminus. CbnY has two α-helices (one hydrophobic, one amphipathic) connected by a short loop and a cationic C terminus. CbnX and CbnY do not appear to interact directly and likely require a membrane-bound receptor to facilitate formation of the bacteriocin complex. This is the first class IIb bacteriocin reported for Carnobacteria.

Leaderless bacteriocins are a class of ribosomally synthesized antimicrobial peptides that are produced by certain Gram-positive bacteria without an N-terminal leader section. These bacteriocins are of great interest due to their potent inhibition of many Gram-positive organisms, including food-borne pathogens such as Listeria and Clostridium spp. We now report the NMR solution structures of enterocins 7A and 7B, leaderless bacteriocins recently isolated from Enterococcus faecalis 710C. These are the first three-dimensional structures to be reported for bacteriocins of this class. Unlike most other linear Gram-positive bacteriocins, enterocins 7A and 7B are highly structured in aqueous conditions. Both peptides are primarily α-helical, adopting a similar overall fold. The structures can be divided into three separate α-helical regions: the N- and C-termini are both α-helical, separated by a central kinked α-helix. The overall structures bear an unexpected resemblance to carnocyclin A, a 60-residue peptide that is cyclized via an amide bond between the C- and N-termini and has a saposin fold. Because of synergism observed for other two-peptide leaderless bacteriocins, it was of interest to probe possible binding interactions between enterocins 7A and 7B. However, despite synergistic activity observed between these peptides, no significant binding interaction was observed based on NMR and isothermal calorimetry.

Phenol-soluble modulins (PSMs) are peptide virulence factors produced by staphylococci. These peptides contribute to the overall pathogenicity of these bacteria, eliciting multiple immune responses from host cells. Many of the α-type PSMs exhibit cytolytic properties and are able to lyse particular eukaryotic cells, including erythrocytes, neutrophils, and leukocytes. In addition, they also appear to contribute to the protection of the bacterial cell from the host immune response through biofilm formation and detachment. In this study, three of these peptide toxins, PSMs α1, α3, and β2, normally produced by Staphylococcus aureus, have been synthesized using solid-supported peptide synthesis (SPPS) (PSMα1 and PSMα3) or made by heterologous expression in Escherichia coli (PSMβ2). Their three-dimensional structures were elucidated using nuclear magnetic resonance spectroscopy. PSMα1 and PSMα3 each consist of a single amphipathic helix with a slight bend near the N- and C-termini, respectively. PSMβ2 contains three amphipathic helices, which fold to produce a "v-like" shape between α-helix 2 and α-helix 3, with α-helix 1 folded over such that it is perpendicular to α-helix 3. The availability of three-dimensional structures permits spatial analysis of features and residues proposed to control the biological activity of these peptide toxins.

The tricyclic peptides neopetrosiamides A and B, isolated from the marine sponge Neopetrosia sp., are potential antimetastatic agents that inhibit tumour cell invasion by both amoeboid and mesenchymal migration pathways. They differ in the stereochemistry of the methionine sulfoxide at position 24. Our previously reported syntheses using an orthogonal sulfur protection strategy established the critical connectivity of the three disulfide bonds. In this report, fifteen analogues of neopetrosiamide A and B, six which replace selected disulfide bonds and nine which replace the diastereomeric methionine sulfoxide, have been prepared using Fmoc solid-phase peptide chemistry. Disulfide replacement analogues were shown to lose activity, and only one of the methionine sulfoxide analogues retained full bioactivity in morphological studies.