Direct analysis of α- and β-chains of hemoglobins from mammalian blood samples by nanoESI mass spectrometry during in-capillary proteolytic digestion

Abstract

α- and β-chains of hemoglobins derived from several species were analyzed directly from diluted blood samples by simultaneous in-capillary proteolytic digestion and nanoESI MS and MS/MS analysis. Starting from fresh or frozen and thawed blood samples, sequence coverages of >80% were usually obtained. Only 2h after resuspension of a dried blood spot, human origin could be demonstrated from data obtained by in-capillary tryptic digestion, nanoESI mass spectrometric analysis, and data base search. A fast and facile differentiation of closely related species by hemoglobin-derived proteolytic "marker peptides" was demonstrated for Asian (Elephas maximus) and African elephants (Loxodonta africana). Finally, amino acid sequences deduced from collision-induced dissociation experiments during in-capillary proteolytic digestion of the corresponding blood samples allowed de novo sequencing of previously unknown sequences of hemoglobin chains of the Patagonian cavy (Dolichotum patagona) and the Persian gazelle (Gazella subgutturosa subgutturosa). 100% of the α-chain sequences and more than 85% of the β-chain sequences were covered for both the species. Additionally, sequence data derived from tandem MS experiments obtained with the Q-Tof analyzer were confirmed by high resolution Fourier-transform ion cyclotron resonance mass spectrometric experiments. Accurate protein mass determination of the intact hemoglobin chains directly from the corresponding blood samples by use of a Fourier-transform ion cyclotron resonance mass spectrometer corroborated the deduced sequences of the respective α-chains. The present study demonstrates that in-capillary digestion allows fast characterization and/or sequencing of hemoglobin chains directly from blood samples.