Mechanistic insights into thrombin's switch between "slow" and "fast" forms

Area of Science:

• Biochemistry
• Molecular Biology
• Computational Biology

Background:

• Thrombin is a key enzyme in blood coagulation, cell growth, and metastasis.
• Thrombin exhibits distinct enzymatic activities, termed 'fast' (sodium-present) and 'slow' (sodium-absent) forms.
• The precise mechanism of sodium ion-mediated functional switching in thrombin remains unclear.

Purpose of the Study:

• To investigate the structural and dynamic differences between sodium-bound/unbound and potassium-bound/unbound thrombin.
• To elucidate the role of cations in modulating thrombin's enzymatic activity.
• To identify the molecular mechanism underlying thrombin's functional switch.

Main Methods:

• Microsecond-scale all-atom molecular dynamics simulations.
• Principal component analysis (PCA) for conformational free energy surface estimation.
• Comparative analysis of sodium and potassium ion binding effects.

Main Results:

• Cation binding significantly impacts regulatory regions like the 60s loop, γ loops, and exosites I and II.
• Multiple conformational states of thrombin exist, influenced by cation binding.
• Sodium ion binding shifts thrombin populations towards catalytically favorable conformations compared to potassium.

Conclusions:

• Sodium ion-mediated generalized allostery is proposed as the mechanism for thrombin's functional switch.
• Understanding cation-specific allostery in thrombin provides insights into enzyme regulation.
• This study offers a molecular basis for the differential activity of thrombin in the presence of sodium ions.