Variability of outer membrane protein P1 and its evaluation as a vaccine candidate against experimental otitis media due to nontypeable Haemophilus influenzae: an unambiguous, multifaceted approach

Candidate vaccine antigens for preventing otitis media caused by nontypeable Haemophilus influenzae (NTHI) should possess one or more conserved epitopes. We sought to evaluate the candidacy of P1, a surface-expressed outer membrane protein knowing that this antigen is subject to diversifying selection. Therefore, we selected NTHI strains from among >500 phylogenically variant isolates representative of the diversity found in natural populations of H. influenzae. Twenty-three variants of P1 (</=95% similarity) were identified among 42 strains. When chinchillas were immunized with recombinant P1 (rP1) obtained from one of these isolates (BCH-3), all animals developed antibodies specific for rP1. Immunized animals were protected against disease when challenged with BCH-3, but not with an ompP1 mutant of BCH-3 or a strain (BCH-2) possessing a heterologous P1 (91% identity). We conclude that (i) while P1 induces protection against NTHI-mediated otitis media, development of a polyvalent vaccine reflecting the variability of P1 would be necessary to construct an efficacious vaccine and (ii) use of a phylogenically characterized collection of representative isolates in concert with gene sequencing, cloning, gene inactivation, and animal testing offers an efficient, rational, and rigorous strategy for evaluating the potential problems associated with variability of vaccine targets and specificity of related immune responses.

Cytochrome P-450terp. Isolation and purification of the protein and cloning and sequencing of its operon

Cytochromes P-450 are extremely important in the oxidative metabolism of a variety of endogenous and exogenous compounds in pro- and eukaryotic organisms. Progress in understanding the structure and mechanism of action of this superfamily of enzymes has been hampered by the properties of the eukaryotic enzymes and the availability of only one well-characterized prokaryotic enzyme as a model. We report here the isolation of a Pseudomonas species which will utilize a monoterpene natural product, alpha-terpineol, as its sole source of carbon and energy. Approximately 1% of the soluble protein in the cell-free extract is a novel cytochrome P-450 (P-450terp). This enzyme and its associated iron sulfur protein electron carrier (terpredoxin) have been purified to homogeneity and their NH2-terminal amino acid sequences determined. The amino acid sequences of six tryptic peptide fragments of cytochrome P-450terp have also been determined. This sequence information was used to clone the gene encoding cytochrome P-450terp. Three clones representing approximately 8 kilobase pairs of unique sequences were selected and sequenced. Five non-overlapping open reading frames (ORFs) were found in the sequences, and the translated sequences were used to search the Protein Identification Resource for comparable proteins. The ORFs were identified as: 1) an alcohol dehydrogenase, 2) an aldehyde dehydrogenase, 3) cytochrome P-450terp, 4) terpredoxin reductase, and 5) terpredoxin. The identification of both the cytochrome P-450terp and terpredoxin DNA sequence was confirmed by the presence of each of the corresponding amino acid sequences found in the purified proteins. The five ORFs were bounded on both the 5' and 3' ends by consensus factor-independent terminator sequences. A consensus promoter sequence was found immediately 5' to the first ORF. These results indicate that we have sequenced the complete terp operon. Comparison of the amino acid sequence of cytochrome P-450terp to that of all other cytochromes P-450 has shown that it is the first member of the gene family CYP108. Preliminary characterization of the chemical and physical properties and the preparation of crystals of this new cytochrome P-450, suitable for x-ray diffraction analysis, indicate that it will be useful in comparison studies with other members of this class of proteins.

Efficient site-directed in vitro mutagenesis using phagemid vectors

Several methods have been developed that enhance the efficiency of in vitro, site-directed mutagenesis. Kunkel (8,9) has developed a method which uses a strong selection for the mutated strand and, hence, is highly efficient, but yet simple and rapid. This method originally used M13 phage as the vector. In this paper, we describe a refinement of this method using phagemid vectors, which combine the advantages of plasmids (such as high copy number and stability of cloned DNA) with the single-stranded DNA generating capability of M13 phage. We demonstrate that high efficiency of mutant production can be obtained with these vectors. We also analyzed by sequencing 11 mutated clones and found no second-site mutations, suggesting that alterations other than the site-directed mutation rarely occur in our system.