Role of native-state structure in rubredoxin native-state hydrogen exchange

Area of Science:

• Biochemistry
• Structural Biology
• Protein Dynamics

Background:

• Rubredoxin from Pyrococcus furiosus (Pf) is a small metalloprotein crucial for electron transfer.
• Protein structure and dynamics are influenced by metal ions and electrostatic interactions.
• Amide hydrogen exchange is a technique used to probe protein structure and conformational changes.

Purpose of the Study:

• To investigate the impact of different metal substitutions (Zn(II), Ga(III), Ge(IV)) on amide exchange rates in Pf rubredoxin.
• To correlate amide exchange kinetics with the electrostatic environment and structural proximity to the active site metal.
• To understand how electrostatic potentials influence protein conformational dynamics and hydrogen exchange.

Main Methods:

• Measurement of base-catalyzed amide hydrogen exchange rates for Pf rubredoxin variants.
• Comparison of exchange rates across proteins with different metal substitutions (Zn(II), Ga(III), Ge(IV)).
• Correlation of exchange rate data with X-ray crystal structures to assess distance dependence.

Main Results:

• Metal substitutions led to up to 3000-fold increases in exchange rates for amides near the active site metal.
• Exchange rate changes were inversely correlated with the distance to the metal ion (up to 12 Å), suggesting electrostatic influence.
• Significant electrostatic potentials within rubredoxin can modulate amide hydrogen exchange rates by over a million-fold.

Conclusions:

• Electrostatic interactions, driven by metal charge and proximity, play a significant role in modulating amide hydrogen exchange rates in Pf rubredoxin.
• The observed distance dependence supports an electrostatic potential-driven shift in amide nitrogen pK as the primary mechanism.
• Residual conformational structure, not just global unfolding, influences hydrogen exchange rates, providing insights into transient protein states.