Identification and Quantification of Any Isoforms of Carbohydrates by 2D UV-MS Fingerprinting of Cold Ions

Biological functionality of isomeric carbohydrates may differ drastically, making their identifications indispensable in many applications of life science. Because of the large number of isoforms, structural assignment of saccharides is challenging and often requires a use of different orthogonal analytical techniques. We demonstrate that isomeric carbohydrates of any isoforms can be distinguished and quantified using solely the library-based method of 2D ultraviolet fragmentation spectroscopy-mass spectrometry (2D UV-MS) of cold ions. The two-dimensional "fingerprint" identities of UV transparent saccharides were revealed by photofragmentation of their noncovalent complexes with aromatic molecules. We assess the accuracy of the method by comparing the known relative concentrations of isomeric carbohydrates mixed in solution with the concentrations that were mathematically determined from the measured in the gas-phase fingerprints of the complexes. For the tested sets with up to five isomers of di- to heptasaccharides, the root-mean-square deviation of 3-5% was typically achieved. This indicates the expected level of accuracy in analysis of unknown mixtures for isomeric carbohydrates of similar complexity.

Identification of isoforms of aspartic acid residues in peptides by 2D UV-MS fingerprinting of cold ions

We use 2D UV-MS cold-ion spectroscopy for the identification of l-Asp, d-Asp, l-isoAsp and d-isoAsp residues in a fragment peptide derived from the hormone protein amylin.

RePLiCal: A QconCAT Protein for Retention Time Standardization in Proteomics Studies

This study introduces a new reversed-phase liquid chromatography retention time (RT) standard, RePLiCal (Reversed-phase liquid chromatography calibrant), produced using QconCAT technology. The synthetic protein contains 27 lysine-terminating calibrant peptides, meaning that the same complement of standards can be generated using either Lys-C or trypsin-based digestion protocols. RePLiCal was designed such that each constituent peptide is unique with respect to all eukaryotic proteomes, thereby enabling integration into a wide range of proteomic analyses. RePLiCal has been benchmarked against three commercially available peptide RT standard kits and outperforms all in terms of LC gradient coverage. RePLiCal also provides a higher number of calibrant points for chromatographic retention time standardization and normalization. The standard provides stable RTs over long analysis times and can be readily transferred between different LC gradients and nUHPLC instruments. Moreover, RePLiCal can be used to predict RTs for other peptides in a timely manner. Furthermore, it is shown that RePLiCal can be used effectively to evaluate trapping column performance for nUHPLC instruments using trap-elute configurations, to optimize gradients to maximize peptide and protein identification rates, and to recalibrate the m/z scale of mass spectrometry data post-acquisition.