Figure 2

Principles behind combinatorial peptidomics. Sample is proteolytically digested, but the affinity purification step of the peptidomics approach [8] is substituted by quantitative depletion of the peptide pools through chemical crosslinking of a subset of peptides (through their amino acid side chains) to a solid support (e.g. derivatised beads, derivatised capillaries, etc). Sulfhydryl groups of Cysteines, Thioether groups of Methionines, Imidazolyl groups of Histidines, Guanidinyl groups of Arginines, Phenolic groups of Tyrosines and Indolyl groups of Tryptophans can be used to covalently immobilise respective amino acids (and peptides which contain them) in a specific and fully predictable manner with respect to amino acid content. Any combination of such amino acid "filters" of various specificities or reactivities is possible (can be used sequentially or as a single "filter" with mixed specificity). Chemical depletion reduces the complexity of a peptide pool to a required degree to make it compatible with direct MS detection.