A multiway approach for classification and characterization of rabbit liver apothioneins by CE-ESI-MS

Abstract

We applied a multiway approach to extract information from the analysis of protein isoform by CE-ESI-MS. Metallothioneins (MT) are low-molecular-weight proteins (6-7 kDa) with a strong affinity for heavy-metal ions. Rabbit liver MT-I and MT-II fractions are purified from MT samples. At low pH, the bound metal ions were released from the amino acid structures, giving rise to apothioneins. MT-I, MT-II and MT apothioneins, which are complex mixtures of protein isoforms, were analyzed by CE-ESI-MS. After data pre-prorcessing, parallel factor-analysis (PARAFAC) and multivariate curve resolution-alternating least squares (MCR-ALS) were applied to the data sets. In both cases, the models enabled classification of the protein samples and identification of their characteristic sub-isoforms using a set of three components. MCR-ALS required an initial estimate of the pure mass spectra of the three components. Thus, PARAFAC loadings were used to initialize the MCR-ALS optimization. The classifications obtained with MCR-ALS were slightly better than those obtained with PARAFAC, probably because MCR-ALS was less affected by the small migration time shifts of the preprocessed electropherograms. However, no differences were found between the pure mass spectra of the three components in either model. Finally, MCR-ALS allowed us to obtain an individual electrophoretic profile of each of the three components for each of the samples analyzed, which proved valuable for characterization and quantification purposes. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.