April 2021 Issue
Quantifying Positional Isomers (QPI) by Top-Down Mass Spectrometry
In Brief Here we determine the quantities of the same protein modified differentially by PTMs, creating so-called positional isomers (i.e., double phosphorylation, one isomer with positions Y64 and T98, and one isomer with positions Y64 and Y120). Knowledge of the relative abundances of these separate positional isomers is highly relevant, as researchers uncovered many thousands of phosphorylation sites many of which have no clear biological function. Uncovering their relative abundance will assist in determining the relative importance of each modification site.Stable Isotope Labeling of Amino Acids in Flies (SILAF) Reveals Differential Phosphorylation of Mitochondrial Proteins Upon Loss of OXPHOS Subunits
In Brief We advanced a fully composed food source for Drosophila melanogaster into a highly efficient, versatile, and cheap labeling method, termed SILAF. The larval proteome incorporates more than 99% heavy lysine-6 label within 6 days, while the adult fly metabolism allows protein turnover studies. We obtained a phosphoproteome with site-specific occupancy in a fly model of mitochondrial metabolic disease, highlighting the regulation of two novel conserved phosphosites on subunits of the electron transport chain.
