Enterococcus faecalis is a Gram-positive, commensal bacterium that lives in the gastrointestinal tracts of humans and other mammals. It causes severe infections because of high antibiotic resistance. E. faecalis can endure extremes of temperature and pH. Acyl carrier protein (ACP) is a key element in the biosynthesis of fatty acids responsible for acyl group shuttling and delivery. In this study, to understand the origin of high thermal stabilities of E. faecalis ACP (Ef-ACP), its solution structure was investigated for the first time. CD experiments showed that the melting temperature of Ef-ACP is 78.8°C, which is much higher than that of Escherichia coli ACP (67.2°C). The overall structure of Ef-ACP shows the common ACP folding pattern consisting of four ␣-helices (helix I (residues 3-17), helix II (residues 39 -53), helix III (residues 60 -64), and helix IV (residues 68 -78)) connected by three loops. Unique Ef-ACP structural features include a hydrophobic interaction between Phe 45 in helix II and Phe 18 in the ␣ 1 ␣ 2 loop and a hydrogen bonding between Ser 15 in helix I and Ile 20 in the ␣ 1 ␣ 2 loop, resulting in its high thermal stability. Phe 45 -mediated hydrophobic packing may block acyl chain binding subpocket II entry. Furthermore, Ser 58 in the ␣ 2 ␣ 3 loop in Ef-ACP, which usually constitutes a proline in other ACPs, exhibited slow conformational exchanges, resulting in the movement of the helix III outside the structure to accommodate a longer acyl chain in the acyl binding cavity. These results might provide insights into the development of antibiotics against pathogenic drug-resistant E. faecalis strains.

Ambient urban particulate matter (PM) contains various transition metals. When the PM is inhaled into the lung, not all but some part of metals from the particles might be mobilized to participate in a reaction that can damage various biomolecules, such as DNA and proteins. The dust particle size as well as organic acids may influence the metal mobilization. Thus, the mobilization of the metal from two standard reference materials (SRM; NIST, USA) and urban PM (PM2.5 and PM10) collected in the Seoul area was measured in the presence of artificial or biological chelator with or without reductant. The degree of the mobilization was higher with the artificial or biological chelator than the control with saline. In some cases, a reductant increased the mobilization as much as about 5 times the control without the reductant. Especially, the mobilization of Fe was greatly influenced by the presence of reductants. In general, the degree of the mobilization of the transition metal was higher with PM2.5 than with PM10. Therefore, it is expected that, considering the previously known toxicities of the transition metals, PM2.5 is more damaging to various biomolecules than PM10. The results also suggest that not the total amount but the mobilizable fraction of the metal in the ambient PM should be considered with regard to the toxicity of the urban particulate matter.

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This study was performed to examine the in vitro toxicities which are incurred due to the mobilization metals from standard reference material (SRM) 1648, fine (PM 2.5 ), and coarse (PM 10 ) particulate matter collected in Seoul metropolitan area. DNA single strand breaks of approximately 74% and 62% for PM 2.5 and for PM 10 , respectively, were observed in the presence of chelator (EDTA or citrate)/ reductant (ascorbate), as compared to the control by 2% without chelator or reductant. PM 2.5 induced about 40% more carbonyl formation with proteins in the presence of EDTA/ascorbate than PM 10 . Therefore, more damage to biomolecules was incurred upon exposure to PM 2.5 than to PM 10 . The treatment of a specific chelator, desferrioxamine, to the reaction mixture containing chelator plus reductant decreased the extent of damage to DNA to the level of the control, but did not substantially decrease the extent of damage to proteins. This suggests that different arrays of metals were involved in the oxidation of DNA and proteins.