A miniaturized, high-throughput buffer-centric method for protein solubility screening

Efficient access to soluble recombinant proteins remains a major bottleneck in biochemical and structural studies. We describe an aqueous, solvent-centric, fully miniaturized 96-well workflow to screen extraction conditions that preserve soluble recombinant protein during lysis and clarification in a single working day. Liquid-nitrogen-frozen E. coli pellets are cryogenically bead-milled with stainless-steel beads, retaining the native intracellular milieu while ensuring uniform disruption. The resulting wet, frozen cell powder can therefore be extracted with user-defined solvent, enabling systematic exploration of pH, ionic strength, detergents, and chaotropes. Protein solubility is assessed by a 1 {micro}L chromogenic anti-His dot-blot. We demonstrate the use of the protocol by solubilizing a set of highly challenging de novo-generated proteins and show that dot-blot intensity provides a practical semi-quantitative proxy for successful extraction of soluble proteins. We also provide experimentally supported guidelines on the influence of solvent reagents on subsequent steps of protein production, SDS-PAGE, and Ni-NTA purification. This workflow is compatible with upstream genetic solubility-enhancement, chassis- and cultivation-based strategies and enables direct transition from screening hits to scale-up. Because the workflow uses standard molecular biology equipment and inexpensive consumables, it can be readily adopted or automated in most laboratories.