Seamless workflow of hydroxy acid-modified metal oxide chromatography for rapid and sensitive phosphoproteomics sample preparation

Phosphoproteomics by liquid chromatography/tandem mass spectrometry requires efficient phosphopeptide enrichment, but conventional workflows are often time-consuming and prone to sample loss, particularly at low input. Here, we present Rapid Hydroxy Acid-Modified Metal Oxide Chromatography (Rapid HAMMOC), a streamlined, TiO2-based enrichment workflow that features three key improvements. First, we optimized the TiO2 column loading conditions and found that alternative pH-buffering agents and organic solvents, such as sodium bicarbonate combined with ethyl acetate, outperformed the commonly used Tris-based buffer with isopropanol. Second, to minimize sample loss and manual handling in desalting, phosphopeptides eluted under basic conditions were directly loaded onto a dual-membrane StageTip composed of stacked strong anion exchange (SAX) and reversed-phase styrene-divinylbenzene (SDB) membranes (SAX-SDB StageTip). Third, the addition of lauryl maltose neopentyl glycol (LMNG), which is readily removed during desalting, suppressed nonspecific adsorption. Rapid HAMMOC provided markedly improved sensitivity, identifying approximately 5,000 class I phosphosites from 5 g of K562 cell digests, with a median 7.9-fold increase in intensity compared to the original workflow. Rapid HAMMOC also identified, on average, approximately 8,000 class I phosphosites from as little as 0.5 g input from HeLa, A549, and HCT116 cells. Furthermore, coupling Rapid HAMMOC with anti-puromycin immunoprecipitation enabled single-day profiling of nascent polypeptides from ultra-low input samples, yielding 2,310 high-confidence co-translational phosphosites. Beyond providing a practical enrichment workflow, this study offers broadly applicable insights that can be extended to other TiO2-based phosphoproteomic methods.