REPEAT-CONTAINING RNA BINDING PROTEINS OF TRYPANOSOMES

ABSTRACT
Flagellated kinetoplastid protozoans inflict public health hazards and economic burden predominately on
marginalized populations in the developing world. The agents of African human and animal trypanosomiasis,
Trypanosoma brucei sp., cause some of the most-studied, but least manageable and curable parasitic infections.
Failing vector control, lack of vaccines and toxic therapeutics place the onus on identification, molecular
understanding and validation of new drug targets. From the fundamental science perspective, these early
branching Excavata represent valuable models of mitochondrial RNA biology, antigenic variation, host-pathogen
interaction, post-transcriptional regulation, and other processes. Major findings in the previous funding period
position a family of RNA binding pentatricopeptide repeat (PPR, 35 amino acids) proteins as the central conduit
controlling mitochondrial gene expression. The unique ability of helix-turn-helix repeats to assemble into
superhelical arrays recognizing extended and compositionally diverse RNA sequences enables the essential
roles of more than 40 PPRs. Often including trypanosome-specific domains, these RNA “sequence readers”
commit otherwise non-specific modification enzymes to their substrates, or block RNA degradation and
extension. This project will elucidate the mechanisms by which nuclear-encoded PPRs govern mitochondrial
mRNA biogenesis and translation via recruiting enzymatic complexes and ribosomes to transcripts at defined
processing stages. We establish three priority areas focusing on PPRs that enable mRNA 5′ end modification,
3′ adenylation/uridylation, and translation. Building on our recent discoveries of gene-specific transcription
initiation and exonucleolytic pre-mRNA processing, we identified PPR factors acting as “protein cap,” “editing
sensor,” poly(A) binding protein, and potential translational activators. Our goal is to dissect the molecular
machinery integrating these functions and to decipher principles of RNA recognition by repeat-containing
proteins. By elucidating their RNA binding sites, structures, interactions, and outcomes of genetic alteration and
protein engineering, this program builds on our momentum in a significant field and expands the knowledge of
critical pathogen-specific processes.

Grant Number: 5R01AI113157-10
NIH Institute/Center: NIH
Principal Investigator: Inna Afasizheva