Book of Abstracts: Albany 2005

category image Volume 22
No. 6
June 2005

Cryo-EM Study of the 80S Ribosome From Trypanosoma cruzi Reveals Novel rRNA Components

The trypanosomatidae family encompasses a group of flagellated protozoans causing a series of severe diseases: Trypanosoma cruzi, Trypanosoma brucei, and species of Leishmania. They have evolved very differently from bacteria, yeast, and animal cells, and have developed unique cellular and genetic pathways. Trypanosomes possess unusually structured mRNAs, identified as a 39-nucleotide spliced leader (SL) and associated cap-4 structure at the mRNA 5' terminus, as products of a special trans-splicing RNA editing mechanism. Counting on the important role of the mRNA 5'-end during eukaryotic translation initiation, the SL sequence and its associated cap-4 structure have been suggested to play a significant part in the recruitment of the ribosome, possibly involving a novel mechanism of initiation. Here, we present a first look at the structure of the T. cruzi 80S ribosome, obtained by cryo-electron microscopy (cryo-EM). Remarkably, the T. cruzi 80S ribosome possesses unusual structural components, in correlation with the secondary structure of its rRNA and the unusually constructed mRNA. In particular, a large helical structure appears in the small subunit, in the vicinity of the mRNA exit channel. We propose that this novel rRNA structure participates in the direct recognition and interaction with the SL sequence and cap-4 structure of the T. cruzi mRNA.

Haixiao Gao1,*
Maximiliano Juri Ayub3
Mariano J. Levin3
Joachim Frank1,2

Health Research, Inc.
2Wadsworth Center
Empire State Plaza
Albany, New York
12201-0509, USA
3Laboratory of Molecular Biology of Chagas Disease
National Research Council (CONICET)
Dept. FBMC
School of Sciences
University of Buenos Aires
1428 Buenos Aires, Argentina