Ligand-dependent structural changes in the V(1) ATPase from Manduca sexta.

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• The V(1) ATPase is crucial for cellular energy transduction.
• Understanding its regulation by Mg(2+) and nucleotides is key to comprehending its function.
• The tobacco hornworm Manduca sexta provides a model system for studying this enzyme.

Purpose of the Study:

• To elucidate the structural and functional responses of Manduca sexta V(1) ATPase to Mg(2+) and nucleotide binding.
• To investigate the role of methanol as an enhancer in these interactions.
• To characterize conformational changes induced by different nucleotide-bound states.

Main Methods:

• CuCl(2)-induced disulfide formation to map subunit proximity.
• Fluorescence spectroscopy using intrinsic tryptophan fluorescence and a coumarin-based probe (CM).
• Small-angle X-ray scattering (SAXS) to assess overall enzyme structure.

Main Results:

• Nucleotide-dependent cross-linking of V(1) ATPase subunits (A, B, D, E) was observed, particularly with MgADP+Pi.
• A direct cross-link between subunits D and E confirmed their close association.
• Fluorescence spectroscopy revealed distinct spectral shifts and intensity changes upon binding of various Mg(2+)-nucleotide complexes (MgAMP.PNP, MgATP, MgADP+Pi, MgADP).

Conclusions:

• Mg(2+) and nucleotide binding induce significant conformational alterations in the V(1) ATPase.
• The enzyme's subunit interactions and structure are dynamically regulated by these ligands.
• These findings contribute to a deeper understanding of V(1) ATPase mechanism and regulation in Manduca sexta.