In 2020 seven genetic variants of the metabolic enzyme SHMT2 were reported to cause a novel brain and heart developmental syndrome (6). SHMT2 can also moonlight and bind to KIRREL3 (1), a synaptic membrane protein linked to several neurological and cognitive disorders including intellectual disability (ID), neurocognitive delay associated with Jacobsen syndrome, and autism spectrum disorder (ASD) (2¿5).
The aim of this project is to investigate the consequences of these variations on the structural fitness of SHMT2 and on its interaction with KIRREL3.
We will achieve this goal by following a biochemical approach and studying the effects of the mutations in vitro at the molecular and atomic level.
Understanding and possibly discerning the effects of the mutations on the moonlighting or the catalytic functions of metabolic enzymes such as SHMT2 is crucial to direct and develop possible therapeutic interventions.
The project aims at understanding the molecular bases of the newly reported neurodevelopmental syndrome associated to genetic variants of SHMT2 (6). We will achieve this goal by following a biochemical approach and studying the effects of the mutation in vitro at the molecular and atomic level. The first task focuses on dissecting the effects of the mutations on the overall structural stability, oligomeric state and catalytic activity of SHMT2. We know that the switch from a stable and ordered conformation to a more flexible and disordered one affects SHMT2 affinity for its cofactor (PLP) and the catalytic activity. However, the oligomeric state of SHMT2 is also crucial for the protein moonlighting activity that is correlated to its ability to undergo post translational modifications (PTM) and protein-protein interactions (PPI). Therefore, the subtle structural changes introduced by the mutations may not only affect the enzymatic properties of SHMT2 but also the other moonlighting functions, as the interaction with KIRREL3-ICD.
Understanding and possibly separating the effects of the mutations on the moonlighting or the catalytic functions is crucial to direct the therapeutic interventions. Although the symptoms of the syndrome point to multifactorial effects, the results of Task 1 will pave the way for a deeper understanding of the failing pathways involved in the syndrome. Task 2 is somewhat more speculative, but the expected results will be of great interest. The involvement of metabolic enzymes such as SHMT in regulation of other cellular pathways by moonlighting activities is recently emerging as a novel regulatory level that is still mostly shrouded in mystery. The interaction of SHMT2 with KIRREL3 points to a direct involvement of SHMT2 in synaptic development and function by participating in one or more protein-protein complexes. The main aim of Task 2 will be to investigate these interactions as a starting point to understand the mechanism of action of these sophisticated regulatory protein-protein complexes.