| The immunized haemolymph was produced from Musca domestica(House Fly) larvae by inducement of injuring the body wall with a hypodermic needle. A protein with antibacterial activity was purified at the first time and the properties of the protein had been studied. The protein was obtained by means of boiled water bath, CM-Sepharose ion-exchange chromatography and Sephadex G-50 gel filtration. The purified protein moved as a single band in low pH PAGE. Its molecular weight was 12,600 Dalton by SDS-PAGE and its isoelectric point was 9.8 by IEF. Amino acid composition assay showed that it was rich in proline. NR/R 2-dimensional SDS-PAGE proved that the two cysteine residues in the molecule were not engaged in intramolecular disulfide bridge. The far UV CD analysis indicated that the protein contained 26.6% α-helix, 23.7% β-sheet, 49.7% β-turn and random coil at pH7. In the hydrophobic environments similar to the membrane of bacteria cell, the content of a-helix increased and the content of P-sheet decreased. It was inferred that the helix should be important to the antibacterial activity. The protein had broad antibacterial activity against several human pathogens, insect pathogens and non-pathogens, and the activity against gram-positive bacteria was higher than the activity against gram-negative bacteria. It was not a lectin, nor a lysozyme, but an unknown antibacterial protein with high heat-stability, which should belong to the pro-rich antibacterial protein family.
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