Insights into the ATP / GTP selectivity of a GTPase, adenylosuccinate synthetase from Leishmania donovani

• Published in: Biochemical and biophysical research communications 2024-06, Vol.715, p.149975, Article 149975
• Main Authors: Mochi, Jigneshkumar A., Jani, Jaykumar, Tak, Kiran, Pappachan, Anju
• Format: Article
• Language: English
• Subjects: BioD superfamily; G4-G5 connected motif; MD simulations; Nucleotide specificity; Switch loop
• ISSN: 0006-291X; 1090-2104; 1090-2104
• DOI: 10.1016/j.bbrc.2024.149975

Many GTPases have been shown to utilize ATP too as the phosphoryl donor. Both GTP and ATP are important molecules in the cellular environments and play multiple and discrete functional role within the cells. In our present study, we showed that one of the purine metabolic enzymes Adenylosuccinate synthetase from Leishmania donovani (LdAdSS) which belongs to the BioD-superfamily of GTPases can also carry out the catalysis by hydrolysing ATP instead of its cognate substrate GTP albeit with less efficiency. Biochemical and biophysical studies indicated its ability to bind to ATP too but at a higher concentration of ATP compared to that of GTP. Sequence analysis and molecular dynamic simulations suggested that residues of the switch loop and the G4-G5 (593SAXD596) connected motif of LdAdSS plays a role in determining the nucleotide specificity. Though the crucial interaction between Asp596 and the nucleotide is broken when ATP is bound, interactions between the Ala594 and the adenine ring of ATP could still hold ATP in the GTP binding site. The results of the present study suggested that though LdAdSS is GTP specific, it still shows ATP hydrolysing activity. •Leishmania donovani Adenylosuccinate synthetase (LdAdSS), a GTPase can also utilize ATP for phosphoryl transfer onto IMP instead of GTP.•The binding affinity of LdAdSS with GTP is stronger than with ATP.•LdAdSS switch loop assumes a closed catalytically active conformation on GDP binding compared to the partially open conformation on ADP binding.•Residues belonging to the connected G4-G5 motif in LdAdSS may be a determinant of its purine base selectivity.