Hydration and conformational equilibrium in yeast thioredoxin 1: implication for H(+) exchange

Area of Science:

• Biochemistry
• Protein dynamics
• Enzyme mechanisms

Background:

• Thioredoxins possess an ancestral water cavity.
• Aspartic acid (Asp24) in yeast thioredoxin 1 (yTrx1) acts as a proton acceptor.
• The water cavity interacts closely with adjacent protein loops.

Purpose of the Study:

• To investigate the role of Asp24 in modulating yTrx1 loop dynamics.
• To explore the coupling of hydration and conformational motion by Asp24.
• To understand how Asp24 influences catalysis and proton exchange.

Main Methods:

• Site-directed mutagenesis (D24N mutation).
• Hydration measurements.
• Molecular dynamics simulations of wild-type and mutant yTrx1.

Main Results:

• The D24N mutation alters the conformational equilibrium of yTrx1 in both oxidized and reduced states.
• Conformational motion within the water cavity is reduced in the D24N mutant.
• Asn24 is more solvent-exposed than Asp24, and the water cavity is smaller in the mutant.

Conclusions:

• Asp24 plays a dual role: proton acceptance and coupling hydration with conformational motion.
• The conformational equilibrium of yTrx1 is critical for its catalytic mechanism and proton exchange.
• Structural and dynamic changes induced by the D24N mutation provide insights into thioredoxin function.