tRNA Synthetases and Neurodegeneration
The process of deciphering the genetic code to produce protein requires aminoacyl-tRNA (aa-tRNA) which are specific tRNA ligated to their specific amino acid. Each aa-tRNA recognizes their target mRNA codon and allows the correct amno acid to be incorporated into a growing polypeptide chain. An ancient and ubiquitous group of enzymes, the aminoacyl tRNA synthetases (ARS) perform the key task of ligating tRNA with their cognate amino acid. It is therefore surprising that mutations in ARS such as glycl-tRNA synthetase or tyrosyl-tRNA synthetase can lead to the peripheral nerve disorders distal spinal muscular atrophy and Charcot-Mare-Tooth. Understanding why neurons are selectively vulnerable to defects in a critical housekeeping gene will be broadly applicable to a range of common disabling neurodegenerative conditions
Current Research Programme
I am currently establishing an independent group with MRC funding. The main aims of my research are:
- To understand the biophysical consequences of disease causing mutations in ARS
- To use proteomics to learn of non-canonical functions of ARS
- To develop cell culture systems to understand the the physiological and pathophysiological role of ARS
- To develop and use model organism to understand disease natural history and mechanisms
To achieve these aims, we are undertaking a detailed study of Glycyl-tRNA synthetase and known disease causing mutations to answer fundamental questions on the mechanism of nerve degeneration. Glycyl-tRNA synthetase is a homodimer and our work on the crystal structure has shown that the mutations are clustered on the dimer interface. Mutations which disrupt dimerization completely have no activity and yet other mutations have normal activity indicating that disease is not caused by a simple loss of core enzyme function. We are therefore searching for novel binding partners of the synthetase to identify novel functions that may be playing a role in disease pathogenesis.
We also want to understand more about the subcellular localization of GlyRS and how this might be affected by disease. We are using neuronal cell cultures and primary motor neuron cultures to answer these questions using real time imaging.
The Neurobiology of Migraine
The other major area of research for the group is understanding pathogenic mechanism in migraine. Migraine is a common, costly and debilitating condition with a complex genetic aetiology. The genetics basis of typical migraine is mostly unknown but we have identified the first gene underlying typical migraine. We found in a large family with migraine, a frameshift mutation in the gene KCNK18, which encodes a tandem-pore background potassium channel, TRESK. TRESK is highly expressed in dorsal root, trigeminal and autonomic ganglia and to lesser extents in the brain and spinal cord. In vitro electrophysiology demonstrates the mutation, which produces a prematurely truncated protein, causing complete loss of function when expressed alone and a dominant negative effect when expressed with wildtype channels. We believe that loss of TRESK function increases cell excitability and responsiveness and thereby lowers the threshold for migraine development. We are building on these findings to further our understanding of migraine and develop new drug treatments.Zam Cader