Selected plasma-associated molecular species remodel the ABCB1 linker with effects retained under structure-derived tethering

Multidrug resistance mediated by P-glycoprotein/ABCB1 remains a major limitation to chemotherapy, and cold atmospheric plasma has been reported to restore drug sensitivity in resistant cancer models. However, the molecular pathways connecting plasma-associated species to P-glycoprotein regulation remain unclear. Here, we used a two-stage reduced-model strategy to test whether selected plasma-associated molecular species can noncovalently remodel the intrinsically disordered NBD1-TMD2 linker of human ABCB1 and whether phenotypes detected in an unconstrained screening model persist when linker terminal geometry is restricted to a structure-derived range. We first screened the free linker against H2O2, NO, or O2 at three molecular loadings and then repeated the same perturbations under terminal tethering, yielding sixty 100-ns all-atom molecular-dynamics trajectories. The free linker showed species- and loading-dependent chemical susceptibility: high-loading H2O2 produced a coherent restriction-oriented phenotype, whereas low-loading O2 drove a pronounced compact, low-exchange redistribution. Chemical responsiveness was not eliminated by tethering. High-loading H2O2 retained a compact, low-exchange phenotype, and high-loading O2 narrowed the projected conformational ensemble and reduced selected exchange modes. In contrast, the strong low-loading O2 response was largely suppressed, indicating dependence on conformational routes enabled by unconstrained terminal motion. Across conditions, responses were spatially heterogeneous; total species-linker attraction did not predict remodeling magnitude, whereas intramolecular H-bond-network reorganization tracked conformational restriction more closely. Together, these simulations establish chemical susceptibility of the ABCB1 linker while distinguishing mechanically persistent from free-motion-dependent responses. The persistent phenotypes provide candidates for testing in full-length transporter simulations and functional assays of ATPase-transport coupling and drug efflux.