Biology subjects

Rosas-Lemus, M.

Publications and source records attributed to Rosas-Lemus, M..

3 recordsLinked to original sources

bioRxiv2021

Mn2+ coordinates Cap-0-RNA to align substrates for efficient 2'-O-methyl transfer by SARS-CoV-2 nsp16

Capping viral messenger RNAs is essential for efficient translation and prevents their detection by host innate immune responses. For SARS-CoV-2, RNA capping includes 2'-O-methylation of the first ribonucleotide by methyltransferase nsp16 in complex with activator nsp10. The reaction requires substrates, a short RNA and SAM, and is catalyzed by divalent cations, with preference for Mn2+. Crystal structures of nsp16-nsp10 with capped RNAs revealed a critical role of metal ions in stabilizing interactions between ribonucleotides and nsp16, resulting in precise alignment of the substrates for methyl transfer. An aspartate residue that is highly conserved among coronaviruses alters the backbone conformation of the capped RNA in the binding groove. This aspartate is absent in mammalian methyltransferases and is a promising site for designing coronavirus-specific inhibitors.

microbiology↗

bioRxiv2020

Methylation of RNA Cap in SARS-CoV-2 captured by serial crystallography

The genome of the SARS-CoV-2 coronavirus contains 29 proteins, of which 15 are nonstructural. Nsp10 and Nsp16 form a complex responsible for the capping of mRNA at the 5' terminus. In the methylation reaction the S-adenosyl-L-methionine serves as the donor of the methyl group that is transferred to Cap-0 at the first transcribed nucleotide to create Cap-1. The presence of Cap-1 makes viral RNAs mimic the host transcripts and prevents their degradation. To investigate the 2'-O methyltransferase activity of SARS-CoV-2 Nsp10/16, we applied fixed-target serial synchrotron crystallography (SSX) which allows for physiological temperature data collection from thousands of crystals, significantly reducing the x-ray dose while maintaining a biologically relevant temperature. We determined crystal structures of Nsp10/16 that revealed the states before and after the methylation reaction, for the first time illustrating coronavirus Nsp10/16 complexes with the m7GpppAm2'-O Cap-1, where 2'OH of ribose is methylated. We compare these structures with structures of Nsp10/16 at 297 K and 100 K collected from a single crystal. This data provide important mechanistic insight and can be used to design small molecules that inhibit viral RNA maturation making SARS-CoV-2 sensitive to host innate response.

molecular biology↗

bioRxiv2020

Structure of SARS-CoV-2 2'-O-methyltransferase heterodimer with RNA Cap analog and sulfates bound reveals new strategies for structure-based inhibitor design

There are currently no antiviral therapies specific against SARS-CoV-2, the virus responsible for the global pandemic disease COVID-19. To facilitate structure-based drug design, we conducted an X-ray crystallographic study of the nsp16/nsp10 2'-O-methyltransferase complex that methylates Cap-0 viral mRNAs to improve viral protein translation and to avoid host immune detection. Heterodimer structures are determined with the methyl donor S-adenosylmethionine (SAM), the reaction product S-adenosylhomocysteine (SAH) or the SAH analog sinefungin (SFG). Furthermore, structures of nsp16/nsp10 with the methylated Cap-0 analog (m7GpppA) and SAM or SAH bound were obtained. Comparative analysis revealed flexible loops in open and closed conformations at the m7GpppA binding pocket. Bound sulfates in several structures suggested the location of the phosphates in the ribonucleotide binding groove. Additional nucleotide binding sites were found on the face of the protein opposite the active site. These various sites and the conserved dimer interface could be exploited for development of antiviral inhibitors.

microbiology↗