Scientific Reports (Apr 2022)

Phosphate-regulated expression of the SARS-CoV-2 receptor-binding domain in the diatom Phaeodactylum tricornutum for pandemic diagnostics

  • Samuel S. Slattery,
  • Daniel J. Giguere,
  • Emily E. Stuckless,
  • Arina Shrestha,
  • Lee-Ann K. Briere,
  • Alexa Galbraith,
  • Stephen Reaume,
  • Xenia Boyko,
  • Henry H. Say,
  • Tyler S. Browne,
  • Mallory I. Frederick,
  • Jeremy T. Lant,
  • Ilka U. Heinemann,
  • Patrick O’Donoghue,
  • Liann Dsouza,
  • Steven Martin,
  • Peter Howard,
  • Christopher Jedeszko,
  • Kinza Ali,
  • Garth Styba,
  • Martin Flatley,
  • Bogumil J. Karas,
  • Gregory B. Gloor,
  • David R. Edgell

DOI
https://doi.org/10.1038/s41598-022-11053-7
Journal volume & issue
Vol. 12, no. 1
pp. 1 – 15

Abstract

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Abstract The worldwide COVID-19 pandemic caused by the SARS-CoV-2 betacoronavirus has highlighted the need for a synthetic biology approach to create reliable and scalable sources of viral antigen for uses in diagnostics, therapeutics and basic biomedical research. Here, we adapt plasmid-based systems in the eukaryotic microalgae Phaeodactylum tricornutum to develop an inducible overexpression system for SARS-CoV-2 proteins. Limiting phosphate and iron in growth media induced expression of the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein from the P. tricornutum HASP1 promoter in the wild-type strain and in a histidine auxotrophic strain that alleviates the requirement for antibiotic selection of expression plasmids. The RBD was purified from whole cell extracts (algae-RBD) with yield compromised by the finding that 90–95% of expressed RBD lacked the genetically encoded C-terminal 6X-histidine tag. Constructs that lacked the TEV protease site between the RBD and C-terminal 6X-histidine tag retained the tag, increasing yield. Purified algae-RBD was found to be N-linked glycosylated by treatment with endoglycosidases, was cross-reactive with anti-RBD polyclonal antibodies, and inhibited binding of recombinant RBD purified from mammalian cell lines to the human ACE2 receptor. We also show that the algae-RBD can be used in a lateral flow assay device to detect SARS-CoV-2 specific IgG antibodies from donor serum at sensitivity equivalent to assays performed with RBD made in mammalian cell lines. Our study shows that P. tricornutum is a scalable system with minimal biocontainment requirements for the inducible production of SARS-CoV-2 or other coronavirus antigens for pandemic diagnostics.