Solution Secondary Structure of a Bacterially Expressed Peptide from the Receptor Binding Domain ofPseudomonas aeruginosaPili Strain PAK: A Heteronuclear Multidimensional NMR Study

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Abstract
The C-terminal receptor binding region of Pseudomonas aeruginosa pilin protein strain PAK (residues 128−144) has recently been the target for the design of a synthetic peptide vaccine effective against multiple strains of P. aeruginosa infection. We have successfully cloned and bacterially expressed a 15N-labeled PAK pilin peptide spanning residues 128−144 of the intact PAK pilin protein, PAK 128−144(Hs145), and have determined the solution secondary structure of this peptide using heteronuclear multidimensional NMR spectroscopy. The oxidized recombinant peptide exists as a major (trans) and minor (cis) species in solution, arising from isomerization around the Ile138−Pro139 peptide bond. The pattern of NOEs, temperature coefficients, and coupling constants observed for the trans isomer demonstrate the presence of a type I β-turn and a type II β-turn spanning Asp134-Glu-Gln-Phe137 and Pro139-Lys-Gly-Cys142, respectively. This is in agreement with the NMR solution structure of the trans isomer of a synthetic PAK 128−144 peptide which showed a type I and a type II β-turn in these same regions of the sequence [McInnes, C., Sönnichsen, F. D., Kay, C. M., Hodges, R. S., and Sykes, B. D. (1993) Biochemistry 32, 13432−13440; Campbell, A. P., McInnes, C., Hodges, R. S., and Sykes, B. D. (1995) Biochemistry 34, 16255−16268]. The pattern of NOEs, temperature coefficients, and coupling constants observed for the cis isomer also demonstrate a type II β-turn spanning Pro139-Lys-Gly-Cys142, but suggest a second β-turn spanning Asp132-Gln-Asp-Glu135. Thus, the cis isomer may also possess a double-turn motif (like the trans isomer), but with different spacing between the turns and a different placement of the first turn in the sequence. The discovery of a double-turn motif in the trans (and cis) recombinant PAK pilin peptide is an extremely important result since the double turn has been implicated as a structural requirement for the recognition of both receptor and antibody. These results pave the way for future isotope-edited NMR studies of the labeled recombinant PAK pilin peptide bound to antibody and receptor, studies integral to the design of an effective synthetic peptide vaccine.