Vitamin D-inducible Antimicrobial Peptide LL-37 binds SARS-CoV-2 Spike and Open Reading Frame Proteins 7a and 8

Annika Roth¹Steffen Lütke¹Matthias Mörgelin²Denise Meinberger¹Gabriele Hermes¹Manuel Koch^1,3Gerhard Sengle^1,3,4Marco Drexelius⁵Ines Neundorf⁵Jan Gebauer⁵Dzemal Elezagic^1*Mats Paulsson^1,3Thomas Streichert¹Andreas R. Klatt¹

• ¹Universitatsklinikum Koln, Cologne, Germany
• ²Lunds Universitet, Lund, Sweden
• ³University of Cologne Center for Molecular Medicine Cologne, Cologne, Germany
• ⁴Universitat zu Koln Institut fur Biochemie, Cologne, Germany
• ⁵Universitat zu Koln Zentrum Biochemie, Cologne, Germany

Background: The role of vitamin D in Coronavirus Disease 2019 (COVID-19) outcomes remains debated, but emerging evidence suggests it may enhance recovery by strengthening immune responses. Vitamin D upregulates LL-37, an antimicrobial peptide with broad antiviral activity, including potential benefits against SARS-CoV-2. LL-37's interactions with viral proteins, however, remain incompletely understood. Methods: We investigated LL-37's interactions with the SARS-CoV-2 Spike glycoprotein and the accessory proteins ORF7a and ORF8 using surface plasmon resonance and negative-stain electron microscopy. These approaches were employed to assess LL-37's binding capabilities and potential impact on viral infectivity. Results: LL-37 bound multiple domains of the Spike protein and inhibited its interaction with the human angiotensin-converting enzyme 2 (hACE2) receptor in vitro. Up to seven LL-37 molecules were observed surrounding Spike, forming a halo-like structure that may block receptor engagement. LL-37 also bound to ORF7a and ORF8, potentially impairing their ability to disrupt host cell processes. Notably, LL-37's interaction with ORF7a may prevent degradation of SNAP29, restoring autophagy and promoting viral clearance. Conclusions: LL-37 disrupts key viral-host interactions by binding to Spike, ORF7a, and ORF8, thereby reducing SARS-CoV-2 infectivity. These findings highlight LL-37's potential as a therapeutic agent in COVID-19 and provide mechanistic insight into its antiviral actions.