The Electronic and Superconducting Properties of Oxygen-Ordered MgB2 compounds of the form Mg2B3Ox

Possible candidates for the Mg2B3Ox nanostructures observed in bulk of polycrystalline MgB2 (Ref.1) have been studied using a combination of Z-contrast imaging, electron energy loss spectroscopy (EELS) and first-principles calculations. The electronic structures, phonon modes, and electron phonon coupling parameters are calculated for two oxygen-ordered MgB2 compounds of composition Mg2B3O and Mg2B3O2, and compared with those of MgB2. We find that the density of states for both Mg2B3Ox structures show very good agreement with EELS, indicating that they are excellent candidates to explain the observed coherent oxygen precipitates. Incorporation of oxygen reduces the transition temperature and gives calculated TC values of 18.3 K and 1.6 K for Mg2B3O and Mg2B3O2, respectively.Comment: Submitted to PR

Identification and crystallisation of a heat- and protease-stable fragment of the bacteriophage T4 short tail fibre

Irreversible binding of Teven bacteriophages to Escherichia coli is mediated by the short tail fibres, which serve as inextensible stays during DNA injection. Short tail fibres are exceptionally stable elongated trimers of gene product 12 (gp12), a 56 kDa protein. The Nterminal region of gp12 is important for phage attachment, the central region forms a long shaft, while a Cterminal globular region is implicated in binding to the bacterial lipopolysaccharide core. When gp12 was treated with stoichiometric amounts of trypsin or chymotrypsin at 37 C, an Nterminally shortened fragment of 52 kDa resulted. If the protein was incubated at 56 C before trypsin treatment at 37 C, we obtained a stable trimeric fragment of 3 33 kDa lacking residues from both the N and Ctermini. Apparently, the protein unfolds partially at 56 C, thereby exposing proteasesensitive sites in the Cterminal region and extra sites in the Nterminal region. Welldiffracting crystals of this fragment could be grown. Our results indicate that gp12 carries a stable central region, consisting of the Cterminal part of the shaft and the attached Nterminal half of the globular region. Implications for structure determination of the gp12 protein and its folding are discussed

Crystallization Of The CHAP Domain Of The Endolysin From Staphylococcus Aureus Bacteriophage K

CHAPK is the N-terminal cysteine, histidine-dependent amidohydrolase/peptidase domain (CHAP domain) of the Staphylococcus aureus bacteriophage K endolysin LysK. It is formed from the first 165 residues of LysK and functions by cleaving specific peptidoglycan peptide bonds, causing bacterial lysis. CHAPK can lyse S. aureus when applied exogenously, making it a good candidate for the treatment of multidrug-resistant Staphylococcus aureus infections. Here, the crystallization of CHAPK and the collection of native and derivative data to high resolution, which allowed structure solution, are reported. The structure may help to elucidate the mechanism of action and in the design of chimeric proteins or mutants with improved antibacterial activity

Inhibition of L. monocytogenes Biofilm Formation by the Amidase Domain of the Phage vB_LmoS_293 Endolysin

peer-reviewedListeria monocytogenes is a ubiquitous Gram-positive bacterium that is a major concern for food business operators because of its pathogenicity and ability to form biofilms in food production environments. Bacteriophages (phages) have been evaluated as biocontrol agents for L. monocytogenes in a number of studies and, indeed, certain phages have been approved for use as anti-listerial agents in food processing environments (ListShield and PhageGuard Listex). Endolysins are proteins produced by phages in the host cell. They cleave the peptidoglycan cell wall, thus allowing release of progeny phage into the environment. In this study, the amidase domain of the phage vB_LmoS_293 endolysin (293-amidase) was cloned and expressed in Escherichia. coli(E. coli). Muralytic activity at different concentrations, pH and temperature values, lytic spectrum and activity against biofilms was determined for the purified 293-amidase protein. The results showed activity on autoclaved cells at three different temperatures (20 °C, 37 °C and 50 °C), with a wider specificity (L. monocytogenes 473 and 3099, a serotype 4b and serogroup 1/2b-3b-7, respectively) compared to the phage itself, which targets only L. monocytogenes serotypes 4b and 4e. The protein also inhibits biofilm formation on abiotic surfaces. These results show the potential of using recombinant antimicrobial proteins against pathogens in the food production environment

Submission of structural biology data for review purposes.

The editors discuss the submission of structural biology data