Connecting RNA processing to metabolism, cellular homeostasis and disease

We have recently discovered the first 2’,3’-cyclic phosphatase in human cells. The enzymatic activity has been characterized and its structure revealed in collaboration with Martin Jinek, in Zurich. The novel and unique cyclic phosphatase is able to modulate pre-tRNA splicing and the UPR by hydrolysing the 2’,3’-cyclic phosphate at the end of 5’ tRNA exons and Xbp1-mRNA exons. 

How did enzymes from Earth’s ancient anaerobic history, such as the RNA ligase RTCB, adapt to modern, aerobic environments? We have revealed an unexpected solution: RTCB, the catalytic subunit of the tRNA ligase complex co-evolved with a dedicated oxidoreductase, PYROXD1, which is linked to severe myopathies in humans. Paradoxically, PYROXD1 uses the principal prooxidative cofactor of the cell, NAD(P)+, as the ‘‘private’’ antioxidative protector of RTCB.

We are investigating the molecular mechanisms of Diamond-Blackfan Anemia (DBA), a disease characterized by a lack of red blood cell production which occurs shortly after birth. How and why do mutations in ribosomal proteins lead to this specific loss of red blood cells? We have recruited a family with two children who were diagnosed with DBA where the father carries a dominant mutation for DBA but does not present with the disease. Using a variety of techniques, we have been probing the effects of this particular DBA mutation within cells, and have established ex vivo red blood cell differentiation assays to validate our findings. See www.dbaexperiment.org.

We have identified CLP1 as a human RNA-kinase that phosphorylates siRNAs and tRNA 3’ exon halves at the 5’ end during in vitro pre-tRNA splicing. CLP1 is associated to the tRNA splicing endonuclease (TSEN) complex and is also part of the mRNA 3’ end formation machinery, with a still enigmatic function. Mutations in CLP1 lead to neurological diseases.

The process of pre-tRNA splicing requires removal of a single intron by the TSEN complex and joining of the resulting exon halves. The tRNA ligase activity remained elusive for three decades. In 2011, we identified HSPC117/RTCB as the catalytic subunit of the tRNA ligase complex. To catalyse multiple ligation reactions, the ligase requires Archease – also identified in our laboratory – as a co-factor. In addition, the tRNA ligase complex is responsible for the ligation of Xbp1-mRNA exons during the Unfolded Protein Response.