Expression and Purification of Full-Length hnRNPA2B1 for Biophysical Characterization of Liquid-Liquid Phase Separation

Abstract

Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1) is a multifunctional RNA-binding protein involved in RNA maturation and mRNA transport. It has recently been shown to undergo liquid-liquid phase separation (LLPS), contributing to the assembly of membraneless organelles. Moreover, dysregulation of LLPS is associated with the formation of pathogenic protein aggregates, in which hnRNPA2B1 is frequently found. Despite its biological and pathological relevance, studies on the full-length protein remain limited due to its intrinsically disordered, low-complexity domain, which renders hnRNPA2B1 highly aggregation-prone and difficult to purify. In this study, we report the successful expression and purification of full-length hnRNPA2B1 with high purity and minimal nucleic acid contamination. By optimizing buffer conditions, specifically ionic strength and pH, we maintain the protein in solution following cleavage of its solubility tag. Preliminary in vitro characterization under near-physiological conditions reveals that purified hnRNPA2B1 undergoes LLPS, forming dynamic liquid-like droplets that grow and mature into amorphous aggregates. Our approach provides a robust method for purifying hnRNPA2B1 suitable for LLPS and aggregation studies. This strategy may also be useful to purify other aggregation-prone, intrinsically disordered proteins.