Enrichment of histidine containing peptides by on-line immobilised metal affinity solid-phase extraction capillary electrophoresis-mass spectrometry

Abstract

The analysis and detection of targeted peptides has received due attention in many fields of proteomics research, such as discovery of biomarkers. In this regard, capillary electrophoresis-mass spectrometry (CE-MS) is widely used, however, direct analysis of low-abundance peptides such as histidine-containing peptides (His-peptides) in complex matrixes by CE-MS remains an analytical challenge. In the present study, an immobilised metal affinity solid-phase extraction containing Ni(II) coupled on-line to capillary electrophoresis-mass spectrometry (IMA-SPE-CE-MS) method has been developed to selectively enrich His-peptides from protein tryptic digests and enhance sensitivity. The method was optimised with α-casein and validated with other standard proteins (β-casein and κ-casein). Later, it was applied to an Escherichia Coli (E. Coli) whole cell lysate. IMA-SPE-CE-MS was very selective and allowed an enrichment factor up to 100-fold. The on-line enrichment and separation method coupled to MS detection is straightforward and advantageous over off-line pretreatment methods in terms of simplicity, cost-effectiveness and throughput.