Automated serum peptide profiling using novel magnetic C18 beads off-line coupled to MALDI-TOF-MS.

Serum peptide profiling by MS is an emerging approach for disease diagnosis and biomarker discovery. A magnetic bead-based method for off-line serum peptide capture coupled to MALDI-TOF-MS has been recently introduced. However, the reagents are not available to the general scientific community. Here, we developed a protocol for serum peptide capture using novel magnetic C18 beads, and automated the procedure on a high-throughput magnetic particle processor. We investigated bead equilibration, peptide binding and peptide elution conditions. The method is evaluated in terms of peaks counts and reproducibility of ion intensities in control serum. Overall, the DynaBead-RPC18-based serum sample processing protocol reported here is reproducible, robust and allows for the detection of ˜200 peptides at m/z 800-4000 of serum that was allowed to clot for 1 h. The average intra-experiment %CV of normalized ion intensities for crude serum and 0.5% TFA/0.15% n-octyl glucoside-treated serum, respectively, were 12% (range 2-38%) and 10% (3-21%) and the inter-experiment %CVs were 24% (10-53%) and 31% (10-59%). Importantly, this method can be used for serum peptide profiling by anyone in possession of a MALDI-TOF instrument. In conjunction with the KingFisher® 96, the whole serum peptide capture procedure is high-throughput (˜20 min per isolation of 96 samples in parallel), thereby facilitating large-scale disease profiling studies.

Retrograde labeling of single neurons in conjunction with MALDI high-energy collision-induced dissociation MS/MS analysis for peptide profiling and structural characterization.

To reveal the peptide contents of the visually nonidentifiable neurons from a neuronal circuit of interest, we combined retrograde labeling of neurons with mass spectrometric single cell analysis. We used the neuronal circuit involved in the copulation behavior of a freshwater snail, Lymnaea stagnalis, as a model. Central neurons that control this behavior are known to send their axons to the penis nerve and innervate the penis complex. By retrograde filling from the penis nerve with nickel-lysine, these neurons were selectively labeled darkish blue. Matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometric analyses of single stained neurons in the parietal ganglion from different animals reveal consistently the presence of several molecular ion species in the range of 800-1200 Da. From a single neuron, six molecular ion species were further characterized with MALDI time-of-flight/time-of-flight mass spectrometry, which demonstrates that the peptides are derived from a previously reported -FLRFamide precursor.