Heme binding to the SARS-CoV-2 spike glycoprotein
Samuel L. Freeman, A. Sofia F. Oliveira, Andrea E. Gallio, Annachiara Rosa, Maria K. Simitakou, Christopher J. Arthur, Adrian J. Mulholland, Peter Cherepanov, Emma Lloyd Raven
Abstract
The target for humoral immunity, SARS-CoV-2 spike glycoprotein has become the focus for vaccine research and development. Previous work demonstrated that the N-terminal domain (NTD) of SARS-CoV-2 spike binds biliverdin – a product of heme catabolism – causing a strong allosteric effect on activity of a subset of neutralizing antibodies. Herein, we show that the spike glycoprotein is also able to bind heme ( K D = 0.5 ± 0.2 μM). Molecular modelling indicated that the heme group fits well within the same pocket on the SARS-CoV-2 spike NTD. Lined by aromatic and hydrophobic residues (W104, V126, I129, F192, F194, I203 and L226), the pocket provides a suitable environment to stabilize the hydrophobic heme. Mutagenesis of N121 has a substantive effect on heme binding ( K D = 3000 ± 220 μM), confirming the pocket as a major heme binding location of the viral glycoprotein. Coupled oxidation experiments in the presence of ascorbate indicated that the SARS-CoV-2 glycoprotein is able to catalyze slow conversion of heme to biliverdin. The heme trapping and oxidation activities of the spike may allow the virus to reduce levels of free heme during infection to facilitate evasion of the adaptive and innate immunity.