Exploring the Platelet Proteome via Combinatorial, Hexapeptide Ligand Libraries

A combinatorial ligand library, composed of millions of diverse hexapeptide baits, able to capture and
concentrate the “low-abundance” proteome while drastically cutting the concentration of the most
abundant species, has been applied to the exploration of the soluble platelet proteome. Mass
spectrometry analysis of untreated and library-treated platelets has resulted in the identification of
435 unique gene products. Of those, 147 entries (35% of the total) have not been described among the
list of >1100 proteins in proteomic platelet investigations reported before. In addition, the analysis of
excised spots from two-dimensional electrophoresis analysis allowed 57 other proteins to be added
that were not found in LC−MS analysis, 33 of them not described before in proteomics studies, bringing
the total number of new gene products to 180. Thus, the present data add a non-negligible number of
species for continuing the “cartography” of the proteomic asset of platelets, in view of completing the
mapping procedure for a deeper understanding of the physiology and pathology of this blood cell.
Because the capturing process is performed under physiological conditions, by exploiting, for binding
to the combinatorial library, the native protein configuration, the described technique is not adapted
to capture highly hydrophobic proteins, which need strong denaturing and solubilizing conditions that
are incompatible with our working procedure. Thus, our list reports essentially hydrophilic proteins,
with negative GRAVY indexes.
Keywords: platelet's proteone • combinatorial libraries • hexameric peptide baits