Allosteric regulation of lysine degradation as a novel pathophysiological mechanism in glutaric aciduria type 1

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Project Summary / Abstract In this project, the investigators propose to study the allosteric mechanisms that regulate lysine degradation and gain novel pathophysiological insights into the rare orphan disease glutaric aciduria type 1 (GA1). GA1 is an autosomal recessive inborn error of lysine, hydroxylysine and tryptophan degradation. Patients can present with brain atrophy and macrocephaly and may develop dystonia after acute encephalopathic crises that lead to striatal degeneration. The disorder is caused by a deficiency of glutaryl-CoA dehydrogenase (GCDH), which leads to the accumulation of neurotoxic glutaric acid and 3-hydroxyglutaric acid. GA1 is considered a treatable disorder and therefore included in newborn screening programs in many countries. However, current treatment consists of dietary intervention, carnitine supplementation, and emergency treatment which requires intense efforts from both caregiver, patient and clinical team. It must be meticulously maintained, but in 25% of patients neurological disease still develops with the outcome reflecting historical health inequities and social determinants of disease. Thus, GA1 treatment needs further improvement, but development of new therapies is hampered by limited understanding of pathophysiological mechanisms. In human patients and the GA1 mouse model, symptomatic disease is accompanied by a striking increase in neurotoxic glutaric- and 3- hydroxyglutaric acid accumulation. The investigators hypothesize that the accumulation of toxic metabolites in GA1 due to the deficiency of GCDH is controlled by allosteric regulation of the lysine degradation pathway. In a high throughput screen, they have identified small molecule inhibitors and activators of the lysine-2- oxoglutarate reductase domain (LOR) of 2-aminoadipic semialdehyde synthase (AASS). This led to the discovery of a remarkable potential for allosteric regulation of this key enzyme in lysine degradation. Structural studies revealed two novel allosteric sites in LOR, one able to bind inhibitors, the other binding activators. Therefore the overall objective of this proposal is to understand the allosteric regulation of lysine degradation. In AIM 1, the structural and biochemical mechanisms of allosteric regulation of LOR/AASS will be studied using X-ray crystallography of LOR/AASS in complex with allosteric activators/inhibitors and enzymology. In AIM 2, the biological significance of allosteric regulation of LOR/AASS and its role in determining lysine degradation flux will be studied. The investigators will identify endogenous inhibitors and activators of LOR/AASS, and define the native protein interaction network of AASS. This knowledge will be used to define how this allosteric mechanism controls lysine degradation and contributes to metabolite accumulation in a GA1 cell line model. In AIM 3, neutral activators of LOR/AASS will be developed using a combination of medicinal chemistry and structure-based drug design. The ultimate goal of this project is to better understand the pathophysiology of GA1 and provide new treatment options.