Skin exudates of rainbow trout contain a potent 13.6kDa anti-microbial protein which, from partial internal amino acid sequencing, peptide mass fingerprinting, matrix-associated laser desorption/ionization MS and amino acid analysis, seems to be histone H2A, acetylated at the N-terminus. The protein, purified to homogeneity by ion-exchange and reversed-phase chromatography, exhibits powerful anti-bacterial activity against Gram-positive bacteria, with minimal inhibitory concentrations in the submicromolar range. Kinetic analysis revealed that at a concentration of 0.3μM all test bacteria lose viability after 30min incubation. Weaker activity is also displayed against the yeast Saccharomyces cerevisiae. The protein is salt-sensitive and has no haemolytic activity towards trout erythrocytes at concentrations below 0.3μM. Reconstitution of the protein in a planar lipid bilayer strongly disturbs the membrane but does not form stable ion channels, indicating that its anti-bacterial activity is probably not due to pore-forming properties. This is the first report to show that, in addition to its classical function in the cell, histone H2A has extremely strong anti-microbial properties and could therefore help contribute to protection against bacterial invasion.
- anti-bacterial protein
- mucosal immunity
The partial internal amino acid sequence of histone H2A from trout skin has been deposited in the Swiss-Prot database under accession number P83327.
Abbreviations used: MALDI-TOF MS, matrix-assisted laser desorption/ionization time-of-flight MS; MBC, minimal bactericidal concentration; MIC, minimal inhibitory concentration; MHB, Mueller—Hinton broth; TFA, trifluoroacetic acid; c.f.u., colony-forming units.
- The Biochemical Society, London ©2002