Molecular recognition and induced dimerization of hnRNP A2/B1 truncations by G-quadruplex single strand DNA.

Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) is a multifunctional nucleic acid metabolism regulator with established roles in viral infection and tumorigenesis. However, a critical gap exists between the oligomeric state of hnRNP A2/B1 and its function as a nuclear DNA sensor. To address this gap, we generated full-length hnRNP A2/B1 and three domain-truncated variants (△NLS, RRM-PrLD, RRM-RGG) using SUMO/MBP fusion expression systems. To define the nucleic acid binding and oligomeric properties of these variants, we combined SEC with EMSA and ITC. These analyses revealed that full-length hnRNP A2/B1 forms soluble amorphous aggregates, whereas the truncated variants exist as stable homogeneous monomers under in vitro solution conditions. Additionally, results demonstrated that the RRM-RGG (15-250) variant binds to ssDNA but not dsDNA. Notably, SEC combined with CD and AUC confirmed that RRM-RGG (15-250) truncations undergo homodimerization induced by 12nt and 22nt Guanine quadruplex (G4) structure enriched ssDNA, which is abundant in the genomes of diverse viruses. Structure predictions revealed that the C-terminal PrLD, and NLS domain are intrinsically disordered, a feature potentially underlying the protein's aggregation propensity and crystallization recalcitrance. NPDock simulations demonstrated that G4-structured ssDNA binds and stabilizes the RRM-RGG (15-250) truncation via non-conserved key residues that are distinct from those of other hnRNP family members. This work provides a biophysical basis for hypothesizing that G4-structured ssDNA-dependent dimerization may contribute to the protein's antiviral function, and establishes a biophysical framework to guide future investigations into the protein's antiviral mechanism and the design of rational targeted inhibitors.