Peptide mapping for detecting variants in protein products

The genetic stability of biotechnology production systems is of importance in evaluating the safety and efficacy of protein products. The analysis methods currently available for assessing the genetic stability of such systems are limited by the complexity of the eukaryotic genome and by their inability to predict the effects of post-transcriptional and post-translational events, such as glycosylation or host cell protein level changes, on the protein produced. Therefore, it is important to focus attention on the protein product itself in evaluating product consistency rather than on nucleotide sequence analysis for genetic stability of the production systems involved. Peptide mapping has arisen as the best method for the analysis of proteins as a surrogate measure of genetic stability. This method uses known chemical reactions or enzymes to cleave the protein at specific sites, resulting in discrete peptides whose structure and composition can be readily compared to that of the theoretical protein coded for by the DNA sequence of its gene. Peptide mapping, which is capable of detecting single amino acid changes in a molecule, can also be used for determining glycosylation sites. Peptide mapping requires sophisticated chromatographic techniques and equipment, and is limited to molecules of m.w. of c. 100,000. The method also requires careful validation to limit the potential for misinterpretation of artifactual peaks. Despite its limitations, no better method currently exists to evaluate product consistency and, thereby, the genetic stability of recombinant products.