Imaging phosphorylated peptide distribution in human lens by MALDI MS

Phosphorylation plays vital roles in complex biological processes such as cellular growth, division and signaling transduction. However, due to the low ionization efficiency of phosphorylated peptides, it is still a huge challenge to obtain region-specific phosphorylated peptide distribution by imaging mass spectrometry. To achieve the on-tissue analysis of phosphorylated peptides, we took advantage of a graphene oxide-immobilized enzyme reactor to conduct the in situ digestion, followed by dephosphorylation treatment that removed the phosphate groups and thereby helped to improve the signal intensity of phosphorylated peptides. A visual representation of the phosphoproteome of a human lens was successfully mapped. Results showed that phosphorylated peptides localized mainly in the nucleus region of a healthy lens while the outer cortex is the dominant region for phosphorylated peptides of a cataractous lens.