This study focuses on the analysis of peptides derived from neuromelanin granules (NMGs) isolated from human brain tissue. The methodology involves high-performance liquid chromatography (HPLC) and mass spectrometry to identify proteins present in the NMG samples.
Begin with peptides derived from neuromelanin granules (NMGs) isolated from postmortem human brain tissue.
NMGs, found in dopamine-producing neurons, contain neuromelanin pigment, proteins, and lipids.
Take a high-performance liquid chromatography (HPLC) column containing a silica-based stationary phase functionalized with hydrophobic ligands.
Load the peptides onto the column.
Hydrophobic peptides bind more strongly to the column than hydrophilic ones.
Pass an elution buffer through the column.
Less hydrophobic peptides elute first, while more hydrophobic ones elute later.
The eluted peptides enter the mass spectrometer's electrospray ionization source, where they are ionized into charged peptide ions.
The ionized peptides then enter the mass analyzer, where they get separated based on their mass-to-charge ratios.
A selected peptide ion is directed to the collision cell and fragmented into smaller ions, whose mass-to-charge ratios are measured again.
Finally, the data is compared to a reference database to identify the proteins present in the NMG sample.
After performing tryptic digestion, as described in the text, prepare the sample for HPLC-MS analysis by dissolving 200 to 400 nanograms of sample peptides in a defined volume of 0.1% TFA in inert mass spectrometric glass vial inlets. If concentration determination is not applicable due to a low sample amount, verify identical sample loading by comparing the total ion current.
To begin proteomic raw data analysis, click Load for loading the raw files into the software. Click on Set Experiment to assign the sample names. To define group specific parameters, add the modifications by choosing Deamidation NQ, Oxidation M, and Carbaminomethylation N-Term as variable modifications. And then add Carbaminomethylation C as fixed modification. Choose trypsin as a digestion enzyme in the digestion tab.
In the label-free Quantification tab. Add the option, LFQ. And if more than 10 files are to be processed, choose the fast LFQ option to shorten the processing time. Ensuring that all other group-specific parameters remain in factory settings, proceed to the Global Parameters tab, and add the FASTA file derived from uniprot.org in the Sequences tab. Modify the identifier rule accordingly, and add the taxonomy ID 9606 for Homo sapiens.
For protein quantification, choose unique and razor peptides. Then, add the iBAQ option as a measure for protein quantification in the label-free Quantification tab. Ensure that all other global parameters remain in factory settings, and click on Start. After the analysis has been successfully performed, retrieve the protein group's .txt output.
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