ATP–NGF-complex, but not NGF, is the neuroprotective ligand

We have shown previously that nerve growth factor (NGF) requires only low nanomolar ATP concentrations in the cell culture medium to protect cortical rat neurons (CRN) from cellular damage induced by staurosporine (STS). We have also demonstrated before that NGF and other growth factors form stable non-covalent complexes with ATP. Here we demonstrated that 8N1ATP–NGF, but not NGF, protected CRN against damage. The photo-reactive ATP derivative 8N3ATP was incubated with NGF and was trapped in its position by UV irradiation forming a covalent bond. The cross-link with a molar ratio of 1:1 (8N1ATP:NGF) was confirmed by mass spectrometry. Circular dichroism experiments revealed that 8N1ATP altered the secondary structure of NGF in the same way as ATP did. Covalently bound 8N1ATP–NGF was shown to be stable in the presence of the ATP-hydrolyzing enzyme alkaline phosphatase while the non-covalent ATP–NGF-complex dissociated with the removal of free ATP from the solution. 8N1ATP–NGF protected CRN against damage by STS independently of free ATP in the culture medium. These results suggest that the ATP–NGF-complex, but not NGF, is the active ligand.

► 8N3ATP formed complex with NGF after UV irradiation by covalent binding. ► 8N1ATP–NGF-complex is neuroprotective in the presence of alkaline phosphatase. ► These results suggest that a ATP–NGF-complex but not NGF alone is the active ligand.