Tagging saccharides for signal enhancement in mass spectrometric analysis

• Published in: Journal of mass spectrometry. Vol. 46; no. 3; pp. 247 - 255
• Main Authors: Chang, Yu-Ling, Liao, Sylvain Kuo-Shiang, Chen, Ying-Chu, Hung, Wei-Ting, Yu, Hui-Ming, Yang, Wen-Bin, Fang, Jim-Min, Chen, Chung-Hsuan, Lee, Yuan Chuan
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-03-2011; Wiley
• Subjects: Arginine - chemistry; Biomolecules; bradykinin; Bradykinin - chemistry; Chemistry; Derivatives; Exact sciences and technology; Ionization; MALDI-TOF-MS; Mass spectrometry; Oligomers; Oligosaccharides; Oligosaccharides - chemistry; Organic chemistry; Phenylalanine; phenylenediamine; Phenylenediamines - chemistry; Reactivity and mechanisms; Residues; signal-enhancing tags; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods; Tags; Sialic acid; MALDI-TOF-MS; Peptides; signal-enhancing tags; Oligosaccharide; oligosaccharides; Matrix assisted laser desorption ionization; Derivatization; Amidation; Amination; Tetrapeptide; Time of flight method; phenylenediamine; Bradykinin; Uronic acid; Conjugated compound; Mass spectrometry
• ISSN: 1076-5174; 1096-9888; 1096-9888
• DOI: 10.1002/jms.1887

MALDI-MS provides a rapid and sensitive analysis of large biomolecules such as proteins and nucleic acids. However, oligo- and polysaccharides are less sensitive in MS analysis partly due to their neutral and hydrophilic nature to cause low ionization efficiency. In this study, four types of oligosaccharides including aldoses, aminoaldoses, alduronic acids and α-keto acids were modified by appropriate tags at the reducing termini to improve their ionization efficiency. Bradykinin (BK), a vasoactive nonapeptide (RPPGFSPFR), containing two arginine and two phenylalanine residues turned out to be an excellent MS signal enhancer for maltoheptaose, GlcNAc oligomers and oligogalacturonic acids. In the MALDI-TOF-MS analysis using 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix, the GalA4-BK and GalA5-BK conjugates prepared by reductive amination showed the detection limit at 0.1 fmol, i.e. ∼800-fold enhancement over the unmodified pentagalacturonic acids. The remarkable MS enhancement was attributable to the synergistic effect of the basic arginine residues for high proton affinity and the hydrophobic property phenylalanine residues for facile ionization. A tetrapeptide GFGR(OMe) and an arginine linked phenylenediamine (H₂N)₂Ph-R(OMe) were thus designed to act as potent tags of oligosaccharides in MS analysis. Interestingly, concurrent condensation and lactonization of α2,8-linked tetrasialic acid (SA4) was carried out with (H₂N)₂Ph-R(OMe) to obtain a quinoxalinone derivative, which showed > 200-fold enhancement over unmodified SA4 in the MALDI-TOF-MS analysis. Copyright © 2011 John Wiley & Sons, Ltd.