Indexed on: 10 Jun '18Published on: 10 Jun '18Published in: Rapid Communications in Mass Spectrometry
Depsipeptides, or peptides with a mixture of amide and ester linkages, may have evolved into peptides on primordial Earth. Previous studies on depsipeptides utilized electrospray ionization - ion mobility - quadrupole time-of-flight (ESI-IM-QTOF) tandem mass spectrometry; such analysis was thorough yet time-consuming. Here, a complementary matrix-assisted laser desorption/ionization - time-of-flight (MALDI-TOF) approach was optimized for rapid characterization of depsipeptide length and monomer composition. Depsipeptide mixtures of varying hydrophobicity were formed by subjecting aqueous mixtures of α-hydroxy acids and α-amino acids to evaporative cycles. Ester and amide content of depsipeptides was orthogonally confirmed using infrared spectroscopy. MALDI-TOF analysis was performed on a Voyager DE-STR in reflection geometry and positive ion mode. Optimization parameters included choice of matrix, sample solvent, matrix-to-analyte ratio, and ionization additives. It was determined that evaporated depsipeptide samples should be mixed with 2,5-dihydroxybenzoic acid (DHB) matrix in order to detect the highest number of unique signals. Low matrix-to-analyte ratios were found to generate higher quality spectra, likely due to a combination of matrix suppression and improved co-crystallization. Using this optimized protocol, a new depsipeptide mixture was characterized. Understanding the diversity and chemical evolution of proto-peptides is of interest to origins-of-life research. Here, we have demonstrated MALDI-TOF mass spectrometry can be used to rapidly screen the length and monomer composition of model prebiotic peptides containing a mixture of ester and amide backbone linkages. This article is protected by copyright. All rights reserved.