GAPDH as a new glycosaminoglycan-binding protein in the extracellular matrix and its possible implication in neurodegenerative disorders

BALEANI, MA; CHEHIN, R; AVILA, CL

Jornada; Jornadas Virtuales de la SAB; 2020

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is considered a multifunctional protein due to its ability to perform different functions in addition to its glycolytic role. This functional plasticity is achieved through conformational changes that expose new interaction surfaces with other proteins. In this way, certain glycosaminoglycans, such as heparin, induce the formation of multimeric GAPDH species with the capacity to act as chaperones in the extracellular space, sequestering toxic aggregates of α-synuclein. This proteostatic role can be affected due to changes in the sulphation patterns of glycosaminoglycans that are associated with aging. Therefore, the administration of glycosaminoglycans would represent a new therapeutic strategy for neurodegenerative disorders (ND). However, the anticoagulant effect of heparin, limits their use in long-term treatments.In this work, the binding of glycosaminoglycans to GAPDH is characterized at the molecular level and a method is proposed to reveal the mechanism of formation of the neuroprotective protofiber. First, it was established that the length of the glycosaminoglycan chain influences both its ability to bind to GAPDH as well as to induce its aggregation. We found that a minimum of three saccharides was needed for binding, while a minimum of fifteen units is necessary to induce GAPDH aggregation. For this reason, fondaparinux, a synthetic pentasaccharide, was used as a model molecule to study the binding process of heparin to GAPDH in equilibrium without it evolving towards the formation of protofibers. By means of binding studies based on changes in the intrinsic fluorescence of tryptophan, the dissociation constant (KD) of fondaparinux toGAPDH was established. The value obtained is consistent with a protein with a low affinity for heparin. On the other hand, the structure of the GAPDH protein was resolved in complex with fondaparinux using X-ray crystallography. Through in silico studies, the sulfate groups of glycosaminoglycans relevant for binding could be established based on their relative contribution to binding energy.These results constitute a valuable input on the development of new therapeutic strategies to stop the progression of ND such as Parkinson's disease. The determination of the pharmacophores in the heparin lay the foundations necessary for the design of molecules capable of binding to GAPDH and enhancing its neuroprotective effect of GAPDH in the extracellular space.