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Antimicrobial peptides serve as a first line of innate immune defense against invading organisms such as bacteria and viruses. In this study, we hypothesized that peptides produced by a normal microbial resident of human skin, Staphylococcus epidermidis, might also act as an antimicrobial shield and contribute to normal defense at the epidermal interface. We show by circular dichroism and tryptophan spectroscopy that phenol-soluble modulins (PSMs) gamma and delta produced by S. epidermidis have an alpha-helical character and a strong lipid membrane interaction similar to mammalian AMPs such as LL-37. Both PSMs directly induced lipid vesicle leakage and exerted selective antimicrobial action against skin pathogens such as Staphylococcus aureus. PSMs functionally cooperated with each other and LL-37 to enhance antimicrobial action. Moreover, PSMs reduced Group A Streptococcus (GAS) but not the survival of S. epidermidis on mouse skin. Thus, these data suggest that the production of PSMgamma and PSMdelta by S. epidermidis can benefit cutaneous immune defense by selectively inhibiting the survival of skin pathogens while maintaining the normal skin microbiome.

A new type of manganese-oxidizing enzyme has been identified in two alphaproteobacteria, “ Aurantimonas manganoxydans ” strain SI85-9A1 and Erythrobacter sp. strain SD-21. These proteins were identified by tandem mass spectrometry of manganese-oxidizing bands visualized by native polyacrylamide gel electrophoresis in-gel activity assays and fast protein liquid chromatography-purified proteins. Proteins of both alphaproteobacteria contain animal heme peroxidase and hemolysin-type calcium binding domains, with the 350-kDa active Mn-oxidizing protein of A. manganoxydans containing stainable heme. The addition of both Ca 2+ ions and H 2 O 2 to the enriched protein from Aurantimonas increased manganese oxidation activity 5.9-fold, and the highest activity recorded was 700 μM min −1 mg −1 . Mn(II) is oxidized to Mn(IV) via an Mn(III) intermediate, which is consistent with known manganese peroxidase activity in fungi. The Mn-oxidizing protein in Erythrobacter sp. strain SD-21 is 225 kDa and contains only one peroxidase domain with strong homology to the first 2,000 amino acids of the peroxidase protein from A. manganoxydans . The heme peroxidase has tentatively been named MopA (manganese-oxidizing peroxidase) and sheds new light on the molecular mechanism of Mn oxidation in prokaryotes.

Nine proline-rich peptides ending with a proline-glutamine C terminus in a salivary peptidome were sequenced by matrix-assisted laser desorption ionization time of flight time of flight tandem mass spectrometry. A GPPPQGGRPQ peptide binds gram-positive Propionibacterium acnes and considerably inhibits bacterial growth. The peptide exhibiting innate immunity may be applied for treatment of various P. acnes -associated human diseases.

One advantage of detecting amide H/2H exchange by mass spectrometry instead of NMR is that the more rapidly exchanging surface amides are still detectable. In this study, we present quench-flow amide H/2H exchange experiments to probe how rapidly the surfaces of two different proteins exchange. We compared the amide H/2H exchange behavior of thrombin, a globular protein, and IkappaBalpha, a nonglobular protein, to explore any differences in the determinants of amide H/2H exchange rates for each class of protein. The rates of exchange of only a few of the surface amides were as rapid as the "intrinsic" exchange rates measured for amides in unstructured peptides. Most of the surface amides exchanged at a slower rate, despite the fact that they were not seen to be hydrogen bonded to another protein group in the crystal structure. To elucidate the influence of the surface environment on amide H/2H exchange, we compared exchange data with the number of amides participating in hydrogen bonds with other protein groups and with the solvent accessible surface area. The best correlation with amide H/2H exchange was found with the total solvent accessible surface area, including side chains. In the case of the globular protein, the correlation was modest, whereas it was well correlated for the nonglobular protein. The nonglobular protein also showed a correlation between amide exchange and hydrogen bonding. These data suggest that other factors, such as complex dynamic behavior and surface burial, may alter the expected exchange rates in globular proteins more than in nonglobular proteins where all of the residues are near the surface.