Antigenic mapping of bacterial and animal cytochromes P-450

Continuous B-epitope maps of cytochrome P450cam (CYP101) obtained by peptide scanning: correlation to spatial structure

Protein continuous B-epitopes can be revealed using short synthetic peptides that overlap a known protein sequence. Since the whole protein surface is considered to possess antigenic properties, a question that arises is whether a set of linear B-epitopes determined by peptide scanning correlates with a protein spatial structure. We have chosen cytochrome P450cam (CYP101) of Pseudomonas putida, with known 3D structure, as a template. Sera of two rabbits and antibody egg yolk preparations from three chickens were produced against the P450cam molecule. These polyclonals were analyzed separately in ELISA with 409 overlapping P450cam hexapeptides. The whole set of continuous antigenic sites of P450cam covered about 45% of the P450cam sequence. However, immunodominant sites (those revealed with more than 50% antibody preparations), the so-called "antigenic core," represent only 9% of the protein sequence. While the amount of water-accessible residues in the total antigenic map (42%) was close to that in the whole native P450cam molecule (39%), the amount of water-accessible residues in the antigenic core was significantly higher (64%). These results led to the conclusion that antigenic core epitopes can be associated to the molecular surface, whereas epitopes with low detection frequency may partly correspond to unfolded regions of the protein molecule.

Identification and mapping of linear antigenic determinants of chicken riboflavin carrier protein

All of the possible 212 overlapping octapeptides covering the amino acid sequence of chicken egg white riboflavin carrier protein (RCP) was synthesized on polyethylene rods. To identify the peptides constituting the sequential antigenic epitopes on chicken RCP, a PEPSCAN ELISA was employed where antibodies raised against SDS-treated, reduced and carboxymethylated RCP (RCM-RCP) in mice, rats (n = 4), rabbits and monkeys (n = 3) were used. By this approach, we could identify five sequences on chicken RCP commonly recognized by all the antisera from these species which were spanning the residues 10-17, 42-49, 134-141, 172-179 and 200-207. Analysis of the data for each individual antiserum indicated inter- and intra-species variations with N- and C-terminal shifts in peak reactivity. The present study offers clues for development of potential immunocontraceptive vaccines.

Epitope mapping of cytochrome P450cam (CYP101)

Eighteen linear antigenically active sites were revealed in cytochrome P450 from Pseudomonas putida (P450cam) by hexapeptide scanning. These sites occupy about 31% of the protein sequence. Hexapeptide epitope sequences of P450cam are not found in other cytochromes P450. However, several cytochromes P450 contain shorter fragments of P450cam epitope sequences which may cause weak immune cross-reactions. P450cam antigenic determinants are located generally at the boundaries of secondary structure elements. Mapping of P450cam antigenic determinants on the three-dimensional structure of this protein reveals 14 highly water-accessible antigenic sites and only 1 site (No. 322-327, QMLSGL) which is inaccessible to water. Several functionally important sites and amino acid residues of P450cam are localized within revealed linear epitopes or very close to them. These sites include substrate-binding regions, residues responsible for the putidaredoxin interaction (Arg72, Arg112, Lys314, and Arg364), heme binding (Gln108, Arg112, Asp297, Arg299, and Cys357), and proton translocation (Lys178, Arg186, and Glu366).