Influence of matrix solution conditions on the MALDI-MS analysis of peptides and proteins

Combining avidin-biotin chemistry with matrix-assisted laser desorption/ionization mass spectrometry

Molecular recognition based on the high affinity of avidin for biotin has been combined with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The rich chemistry of biotinylation reagents underlies the development of a mass tracer method for the rapid and sensitive analysis of biotinylated analyte in complex mixtures. In this method, the biotinylated analyte is captured with immobilized avidin agarose beads. The beads with the bound complex are deposited on the MALDI sample probe, followed by elution of the retained compounds and removal of the beads. The use of MALDI matrix solutions in conjunction with drying of the beads is shown to be sufficient to overcome the avidin-biotin interaction. The studies of several different avidin-biotin interaction schemes tailored to the MALDI analysis are presented. It is demonstrated that, with an optimized scheme, the extremely high selectivity of the avidin-biotin interaction is preserved, generating species represented in the MALDI spectra that arise only from the avidin-biotin interaction. Biotinylated species in the nanomolar range can be isolated and analyzed with this technique.

Characterization of protein-hapten conjugates. 2. Electrospray mass spectrometry of bovine serum albumin-hapten conjugates

Fifteen hapten-bovine serum albumin (BSA) conjugates were prepared from five commercially available activated haptens. Each hapten was coupled to BSA at three different ratios. The conjugates were characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and two mass spectrometry (MS) methods: matrix-assisted laser desorption ionization (MALDI) and liquid chromatography-electrospray ionization (LC-ESI). SDS-PAGE was useful in detecting protein cross-linking, but not assessing hapten density. MALDI-MS and LC-ESI-MS gave comparable qualitative results, but LC-ESI-MS provided a clearer representation of the distribution of hapten-protein species present in the conjugates. Conjugate species substitute with up to 25 haptens per BSA were recorded by LC-ESI-MS.