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The venom from the solitary bee Osmia rufa (Hymenoptera: Megachilidae) was analyzed
using mass spectrometry (MS)-based techniques. Sensitive proteomic methods such as
on-line LC-ESI-MS and nanoESI-MS analyses revealed more than 50 different compounds
with molecular masses ranging from 400 to 4000Da. The major component has a monoisotopic
molecular mass of 1924.20Da and its amino acid sequence was elucidated by de novo
sequencing using tandem mass spectrometry and Edman degradation. This 17-residue cysteine-free
peptide, named osmin, shows some similarities with the mast cell degranulation (MCD)
peptide family. Free acid and C-terminally amidated osmins were chemically synthesized
and tested for antimicrobial and haemolytic activities. The synthetic C-amidated peptide
(native osmin) was found to be about three times more haemolytic than its free acid
counterpart, but both peptides are much less lytic than melittin from social bee venom.
Preliminary antimicrobial and antifungal tests indicate that both peptides are able
to inhibit bacterial and fungal growth at micromolar concentrations.