Achieving Augmented Limits of Detection for Peptides with Hydrophobic Alkyl Tags

• Published in: Analytical chemistry (Washington) Vol. 79; no. 11; pp. 3989 - 3995
• Main Authors: Frahm, Jennifer L, Bori, Ibrahim D, Comins, Daniel L, Hawkridge, Adam M, Muddiman, David C
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.06.2007
• Subjects: Acetates - chemistry; Alkylation; Amides - chemical synthesis; Amides - chemistry; Amino Acid Sequence; Aminoacids, peptides. Hormones. Neuropeptides; Analytical chemistry; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Chemical compounds; Chemistry; Chlorides - chemistry; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Hydrophobic and Hydrophilic Interactions; Iodine - chemistry; Mass spectrometry; Molecular Sequence Data; Molecules; Peptides; Peptides - analysis; Peptides - chemistry; Proteins; Proteomics; Sensitivity and Specificity; Spectrometric and optical methods; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry; Cysteine; Peptides; Coupled method; Hydrophobic compound; Hydrophobicity; Droplet; Alkylation; Electrospray; Chemical ionization; Protein; Alkyl; Detection limit; Feasibility; Dissociation; Mass spectrometry
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac070558q

The wide range of protein concentrations found in biological matrixes presents a formidable analytical challenge in proteomics experiments. It is predicted that low-abundance proteins are the likely clinically relevant targets in disease-based proteomics analyses. To effectively analyze low-abundance proteins by electrospray ionization mass spectrometry, limits of detection must be improved upon. Previous studies have demonstrated hydrophobicity is a main determinant of the electrospray ionization response. One would expect to improve the electrospray ionization response of a hydrophilic peptide by making it more hydrophobic, thus increasing the molecule's affinity for the surface of the electrospray droplet, thereby allowing the molecule to more effectively compete for charge. In this report, we demonstrate a strategy to increase the electrospray ionization response of cysteine-containing peptides with the addition of an octylcarboxyamidomethyl modification via alkylation chemistry, which we name the ALiPHAT strategy (augmented limits of detection for peptides with hydrophobic alkyl tags). We demonstrate the relative increase in electrospray ionization response of peptides with an octylcarboxyamidomethyl modification compared to carboxyamidomethyl-modified peptides upon LC−MS analysis. Furthermore, we show the octylcarboxyamidomethyl group does not fragment or undergo neutral loss during collision-induced dissociation. Collectively, our results demonstrate the feasibility of the octylcarboxyamidomethyl modification to improve limits of detection for cysteine-containing peptides.