Poster abstracts

Poster number 149 submitted by Suada Leskaj

Structural characterization of translation initiation on HPV-18 E6 mRNA

Suada Leskaj (Department of Biological Chemistry, University of Michigan), Ritam Neupane (Department of Biological Chemistry, University of Michigan), Andrew Shurer (Department of Biological Chemistry, University of Michigan), Rachel O. Niederer (Department of Biological Chemistry, University of Michigan), Jailson Brito Querido (Department of Biological Chemistry, Life Sciences Institute, University of Michigan)

Abstract:
Human Papillomaviruses (HPVs) are causative agents of nearly all cervical cancers and are implicated in various other human malignancies. It was recently shown that a high-risk strain of HPV (HPV-18) uses mRNA with an extremely short 3 nucleotide ACC 5′-UTR to make the oncogenic protein E6. Canonical models of translation initiation do not readily accommodate ribosomal recruitment to such minimal 5′-UTRs. The precise mechanism by which ribosomes recognize and initiate translation on such minimal 5′-UTRs remains unknown. To investigate translation initiation on a 3-nucleotide 5′-UTR, we in vitro reconstituted human 48S initiation complexes on HPV-18 E6 mRNA and determined the structure by cryo-electron microscopy at 2.9 Å resolution. We captured a late-stage initiation complex in which the initiator tRNA is directly base-paired with the AUG start codon. We observe density 5′ of the start codon that could accommodate the ACC 5′-UTR as well as possible density for the 5′ m7G cap structure. Ongoing refinement of the cap-binding region will clarify whether there is unique mRNA cap–ribosome interactions at play for E6, which may provide further insight into how start site selection and ribosome recruitment are achieved on short 5′-UTRs. These structural insights will advance our understanding of non-canonical translation initiation mechanisms and how they are exploited by viruses.

References:
García, A. et al. High-risk human papillomavirus-18 uses an mrna sequence to synthesize oncoprotein E6 in tumors. Proceedings of the National Academy of Sciences 118, (2021).

Keywords: translation initiation , HPV, cryo-EM