Data-independent acquisition method for ubiquitinome analysis reveals regulation of circadian biology

Protein ubiquitination is involved in virtually all cellular processes. Enrichment strategies employing antibodies targeting ubiquitin-derived diGly remnants combined with mass spectrometry (MS) have enabled investigations of ubiquitin signaling at a large scale. However, so far the power of data independent acquisition (DIA) with regards to sensitivity in single run analysis and data completeness have not yet been explored. Here, we develop a sensitive workflow combining diGly antibody-based enrichment and optimized Orbitrap-based DIA with comprehensive spectral libraries together containing more than 90,000 diGly peptides. This approach identifies 35,000 diGly peptides in single measurements of proteasome inhibitor-treated cells - double the number and quantitative accuracy of data dependent acquisition. Applied to TNF signaling, the workflow comprehensively captures known sites while adding many novel ones. An in-depth, systems-wide investigation of ubiquitination across the circadian cycle uncovers hundreds of cycling ubiquitination sites and dozens of cycling ubiquitin clusters within individual membrane protein receptors and transporters, highlighting new connections between metabolism and circadian regulation. Protein ubiquitylation is often studied by proteomics but how data independent acquisition (DIA) may advance these studies remains to be explored. Here, the authors show that DIA improves ubiquitylation site identification and quantification, enabling them to characterize the circadian ubiquitinome in human cells.

Automated summary

Protein ubiquitination is involved in various cellular processes and investigations on ubiquitin signaling at a large scale have been enabled by enrichment strategies combined with mass spectrometry. A sensitive workflow combining diGly antibody-based enrichment and optimized Orbitrap-based data independent acquisition (DIA) has been developed, allowing identification of a large number of diGly peptides in single measurements. The study demonstrates the potential of DIA in advancing studies on protein ubiquitylation, particularly in characterizing the circadian ubiquitinome in human cells.