Structural Characterization of Selenoprotein S: Its Oligomerization studies and its complex with the SARS-CoV-2 Replication and Transcription Complex

Abstract

Selenoproteins are proteins defined by the presence of the amino acid selenocysteine. While some selenoproteins are well understood, there is limited in-depth knowledge on the structure and cellular roles of membrane-bound selenoproteins – one of which is selenoprotein S (selenos). Selenos is an intrinsically disordered protein primarily bound to the membrane of the endoplasmic reticulum where it participates in the degradation of misfolded proteins, a process called the Endoplasmic Reticulum-Associated protein Degradation (ERAD) pathway. Selenos has also been implicated in cellular signaling and shown to have enzymatic activity in vitro. At the onset of COVID-19, several host-viral interactome studies identified selenos as one of the host proteins that bind SARS-CoV-2 proteins. Notably, our lab recently showed the first biochemical evidence of the interaction between selenos and the replication and transcription complex (RTC) of SARS-CoV-2. However, there is no structural data yet for this interaction; neither is the role of the interaction defined. This thesis provided the groundwork for the structural characterization of the complex formed by selenos and the SARS-CoV-2 minimal RTC. Also, to gain more insight into selenos oligomerization, we also studied, via size-exclusion chromatography, how different protein regions contribute to its oligomerization.