Flagellin inhibits Myoviridae phage phi CTX infection of Pseudomonas aeruginosa strain GuA18: purification and mapping of binding site

phi CTX is a double-stranded DNA phage of the Myoviridae family that conver ts Pseudomonas aeruginosa into a cytotoxin producer. A 42-kDa phi CTX-inhib iting protein was purified from the outer membrane fraction of P. aeruginos a strain GuA18 by octyl-beta -glucoside extraction, DEAE-chromatography, an d mono-Q HPLC. This protein had an isoelectric point of 5.4 and bound speci fically [I-125]-labeled phi CTX. The N-terminal amino acid sequence of six out of seven Lys-C fragments was highly similar (87%) to that of the entire of type-a flagellin of P. aeruginosa strain PAK. At a concentration of 14 nM, purified flagellin protein caused a 50% decrease in the phage titer aft er a 20-min incubation at 37 degreesC (PhI50). The presence of ethanol was necessary to reconstitute the inhibitory activity. In contrast, no ethanol treatment was necessary for the inhibitory activity of the sheared flagelli n filaments from P. aeruginosa strain GuA18, which consists of the 42-kDa f lagellin subunits and the synthesized 17-mer phage-binding-peptide NGSNSDSE RTALNGEAK, representing flagellin residues 100-116 of P. aeruginosa strain PAK. The PhI50 was 10 nM and 200 nM, respectively. Antisera against the fla gellin filament protein as well as against the 17-mer peptide neutralized p hage infection. These results indicated that the amino acid region 100-116 of the flagellin subunit of strain GuA18 is involved in phi CTX binding. Th is region might play a role in phage attachment.