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SARS-CoV-2 Nucleocapsid Protein Is Not Responsible for Over-Activation of Complement Lectin Pathway.

Andrea Kocsis1, Dalma Bartus1, Edit Hirsch2

  • 1Institute of Molecular Life Sciences, HUN-REN Research Centre for Natural Sciences, Hungarian Research Network, H-1117 Budapest, Hungary.

International Journal of Molecular Sciences
|July 13, 2024
PubMed
Summary

The SARS-CoV-2 nucleocapsid protein does not activate the lectin complement pathway. It triggers alternative and classical pathways, but this is due to bound nucleic acids, not the protein itself.

Keywords:
COVID-19MASP-2SARS-CoV-2 nucleocapsid proteincomplement lectin pathwayproteolytic activityzymogen activation

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Area of Science:

  • Immunology
  • Virology
  • Biochemistry

Background:

  • The nucleocapsid (N) protein of SARS-CoV-2 is abundant in infected individuals.
  • Previous studies suggested controversial roles for the N protein in complement system activation, specifically the lectin pathway.
  • It was hypothesized that the N protein interacts with mannose-binding lectin-associated serine protease-2 (MASP-2) to overactivate the lectin pathway.

Purpose of the Study:

  • To investigate the effect of the SARS-CoV-2 N protein on lectin pathway activation.
  • To clarify the mechanism by which the N protein might influence complement activation.
  • To determine if the N protein directly interacts with MASP-2 and MASP-1.

Main Methods:

  • Assays to detect N protein binding to MASP-1 and MASP-2.
  • Measurement of lectin pathway activity in normal human serum with and without N protein.
  • Assessment of MASP-2 zymogen activation and enzymatic activity.
  • Investigation of N protein interaction with alternative and classical complement pathways.
  • Analysis of complement activation triggered by N protein with and without bound nucleic acids.

Main Results:

  • The SARS-CoV-2 N protein does not bind to MASP-1 or MASP-2.
  • N protein does not stimulate lectin pathway activity, facilitate MASP-2 zymogen activation, or enhance MASP-2 enzymatic activity.
  • MASP-2 was observed to digest the N protein, though biological relevance is uncertain.
  • Surface-bound N protein triggered alternative pathway activation in human serum.
  • Classical pathway activation was observed but attributed to bound nucleic acids, not the N protein itself.

Conclusions:

  • The SARS-CoV-2 N protein does not directly activate the lectin complement pathway.
  • The N protein's observed effects on complement are primarily linked to bound nucleic acids, triggering alternative and classical pathways.
  • The findings refute previous suggestions of direct N protein interaction with MASP-2 for lectin pathway overactivation.