Archaeal and viral functional homologs of SIRV2gp21 induce cell gigantism and growth arrest in Sulfolobus islandicus

Abstract

Host-virus interactions in archaea is a topic that still remains little explored. A recent study has revealed that the protein gp21 from SIRV2 (Sulfolobus islandicus rodshaped virus 2) induces cell gigantism and growth arrest in the archaeal host Sulfolobus islandicus LAL14/1 after being overexpressed. Remarkably, homologs of this protein have been found in a wide variety of viruses infecting archaea, and also in the archaeal host itself. The importance of this lies in the fact that gp21 and its homologues share a very well conserved three-dimensional structure with a RHH domain that binds to DNA (β strand–α helix–α helix conformation), suggesting that they act as transcriptional factors.

The aim of this project was to study whether the selected homolog proteins from the host, SiL0190 and SiRe1157, and from different viruses, SIFV0019 from Lipothrixvirus, STIV-A61 from Turrivirus, SMVgp63 from Bicaudavirus, SIRV4gp14 from Usarudivirus and SSV2gp18 from Fusellovirus induced the same phenotype as gp21 after overexpression in S. islandicus LAL14/1. Therefore, the genes encoding these proteins were cloned and transformed into the host, and their expression was induced. The growth of the cells was followed over time by measuring the culture density, and a possible change in the cell phenotype was assessed with fluorescence microscopy and flow cytometry.

This work has demonstrated that the proteins SiL0190, STIV-A61 and SMVgp63 induce the same phenotype as gp21 in S. islandicus LAL14/1: cell gigantism and growth arrest, while SiRe1157 does not significantly affect the phenotype. The remaining proteins were not successfully overexpressed; thus, future experiments will elucidate whether they exhibit the same behaviour as gp21 in regard to the host.

Popular Abstract

Cell gigantism in archaea induced by viral proteins

Viruses are widely spread in nature, presenting very different morphology and genetics among them. The same as some viruses can infect humans, like the coronavirus SARS-CoV-2, animals or bacteria, some others have the ability to exclusively infect archaea.

Archaea are unicellular microorganisms lacking a nucleus, generally found in extreme environments with high temperature and low pH. They are believed to have evolved from the same common ancestor as bacteria and eukaryotes, eventually separating into three different groups. For this reason, they have physical resemblance with bacteria, and share some similarities in their life cycle with eukaryotes.

Recently, it has been discovered that gp21, a protein from a virus that infects archaea (SIRV2), changes the size of the archaea called Sulfolobus islandicus, producing gigantic cells with a 20-fold increase in their diameter, in comparison with non-infected cells. The importance of gp21 relies in the fact that this protein has also been found in a vast variety of viruses infecting archaea, and in the archaeal host itself. Indeed, all of them have a very similar sequence and 3D structure, meaning, they are homolog proteins. Although its function remains still unknown, the presence of the protein in very diverse organisms, and its conserved structure throughout evolution, is indicative of its importance, not only for the viruses, but also for archaea.

Protein gp21 and its homologs induce cell gigantism
The aim of this work was to investigate whether the homologs of gp21 can induce the same phenomenon of cell gigantism, in the same archaeal host. Therefore, 5 viral proteins were selected from Lipothrixvirus, Turrivirus, Rudivirus, Bicaudavirus and Fusellovirus respectively, as well as 2 proteins from the archaea Sulfolobus islandicus (SiL0190 and SiRe1157). Each protein was introduced separately in the archaeal cell by genetic engineering techniques, and the cells were stained and observed under the microscope after 24, 48 and 72h.

It was confirmed that, as hypothesized, the cells infected with the proteins from Turrivirus and Bicaudavirus exhibited the same phenotype produced with gp21. Moreover, SiL0190 of S. islandicus also caused the same phenomenon (Figure 1), while SiRe1157 did not appear to change the cell diameter significantly. The reason why SiL0190, present in the archaea, is causing this cell gigantism is still a topic under study. The remaining viral proteins were not successfully analysed; thus, no conclusive results were obtained. Interestingly, gp21 and its homolog proteins have a very well conserved part in their structure, called RHH domain. This region has previously been associated with transcription factors, whose function is to bind to the DNA and regulate the gene expression. Therefore, since gp21 and its homologs have the same function, producing gigantic cells in archaea, and contain a RHH domain, it is speculated that they bind to the same region in the DNA, regulating the same genes.

Master’s Degree Project in Molecular Biology, 45 credits 2022
Department of Biology, Lund University

Advisor: Xu Peng and Laura Martínez Álvarez
Department of Functional Genomics, Copenhagen Biocenter

• author: Lozano Madueño, Cristina
• supervisor: Xu Peng; Laura Martínez Álvarez
• organization: Degree Projects in Molecular Biology
• course: MOBN02 20212
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9082200
• date added to LUP: 2022-05-31 14:58:04
• date last changed: 2022-05-31 14:58:04