MALDI Imaging Mass Spectrometry Reveals Age-Related Deamidation and Truncation of Human Lens Insoluble Proteins

摘要

MALDI IMS is a powerful technology for mapping the spatial distribution of modified proteins in human lens. AQP0 protein, with and without fatty acid acylation, undergoes age-related truncation. In situ digestion enabled analysis of small m/z posttranslational modifications, as well as imaging of tryptic fragments of larger insoluble lens proteins including crystallins, MP20, and beaded filaments filensin and phakinin. The high mass resolution of the Bruker SolariX 15T FTICR enabled us to resolve and image deamidated peptides for the first time. Un-, singly-, and doubly-deamidated forms of AQP0 239-263 have distinct localization; deamidation precedes truncation at residue 259. LC-MS/MS data from peptide extracts enabled the identification of signals from peptide imaging experiments, including the assignment of deamidation at N246 and N259. These methods are useful for imaging and identifying modified peptides from many large proteins.