Analysis of the amino acid sequence of the Pseudomonas aeruginosa galactophilic PA-I lectin.

Based on the NH2-terminal 30-amino acid sequence of Pseudomonas aeruginosa galactophilic PA-I lectin, two degenerate primer oligonucleotides were synthesized and used in polymerase chain reaction with the bacterial chromosomal DNA as a template. A predominant DNA fragment of the appropriate size was radiolabeled and used as a probe for screening a P. aeruginosa genomic lambda gt11 library. One positive clone carrying an insert of about 630 base pairs encompassing the entire PA-I lectin gene was isolated and found to contain a 369-base pair open reading frame between an initiation codon (19 base pairs downstream from the insertion site, subsequent to a Shine-Dalgarno sequence) and two consecutive stop codons, followed by an oligo (seven) A sequence, in a partial dyad symmetry. The deduced amino acid sequence shows excellent agreement with the quantitative amino acid analysis and a perfect match with the NH2-terminal amino acid sequence of the purified lectin. It reveals that the PA-I lectin subunit contains 121 amino acids (M(r) 12,754; pI 4.94) with a predominant central hydrophilic core between two hydrophobic domains. Secondary structure algorithms predict that it is rich in beta sheets and contains several highly antigenic epitopes, but no signal peptide. In the carboxyl region a potential glycosylation site (Asn-Asn-Ser) was identified. Comparative analyses of this lectin sequence with those of lectins from other sources, reported in the protein and gene data banks, did not reveal any extensive homology.