Conformational changes in proteins induced by dynamic associations. A tryptophan phosphorescence study

Area of Science:

• Biochemistry
• Protein Dynamics
• Enzyme Kinetics

Background:

• Macromolecular collisions can lead to transient associations, potentially affecting protein conformation and enzyme activity.
• The phosphorescence lifetime of tryptophan (Trp) is sensitive to the internal flexibility of globular proteins.

Purpose of the Study:

• To investigate structural perturbations in alcohol dehydrogenase (LADH) and glyceraldehyde-3-phosphate dehydrogenase (GraPDH) induced by other proteins in solution.
• To explore potential intermolecular communication between proteins using Trp phosphorescence lifetime.

Main Methods:

• Probing protein structure and flexibility via phosphorescence lifetime measurements of tryptophan residues.
• Analyzing the effect of varying concentrations of different proteins (dehydrogenases and unrelated proteins) on Trp phosphorescence lifetime.
• Investigating potential quenching mechanisms by examining cysteine, cystine, and N-acetyl-tryptophanamide.

Main Results:

• Addition of other proteins to LADH caused a reduction in phosphorescence lifetime, quantified by Stern-Volmer rate constants.
• Ternary complex formation with LADH ligands decreased these rate constants.
• Similar effects were observed with GraPDH, with some interactions exhibiting hyperbolic behavior and apparent dissociation constants.
• Glycerol-3-phosphate dehydrogenase showed varied effects on different dehydrogenases, while indole groups were identified as potential quenchers.

Conclusions:

• The study confirms a subtle form of communication between protein molecules in solution.
• These perturbations are likely not related to direct coenzyme transfer due to lack of specificity.
• Protein-protein interactions in solution can dynamically modulate enzyme structure and function.