Heparin interactions with phospholipid and cholesterol monolayers mimicking SARS-CoV-2 envelope and host membranes: A Langmuir film approach.

Understanding how heparin modulates membrane interactions relevant to SARS-CoV-2 entry is essential for elucidating its antiviral mechanisms. Here, Langmuir monolayers were used as biomimetic models of viral and host membranes to investigate interactions with the spike receptor-binding domain (RBD), ACE2, and heparin. Surface pressure-area isotherms, dilatational rheology, Brewster angle microscopy, and PM-IRRAS revealed lipid-dependent effects. In viral-model monolayers, RBD and heparin significantly disrupted film organization, decreasing elasticity and increasing dissipative behavior, with the RBD-heparin complex producing the most pronounced fluidization despite increased local chain order. In host-model monolayers, ACE2 was the main perturbing agent, while heparin primarily interacted with ACE2 without major additional disruption; subsequent RBD addition induced moderate structural reorganization. Notably, opposing trends between compressional and dynamic moduli highlight distinct relaxation regimes governing interfacial mechanics. Overall, heparin acts as a membrane-active modulator, altering interfacial organization and mechanics in a lipid-dependent manner. These findings suggest that, beyond direct protein binding, heparin may interfere with SARS-CoV-2 infection through membrane-mediated mechanisms.