Significant Loop Motions in the SsoPTP Protein Tyrosine Phosphatase Allow for Dual General Acid Functionality

Area of Science:

• Enzymology
• Structural Biology
• Biochemistry

Background:

• Conformational dynamics are crucial for enzyme function, particularly in protein tyrosine phosphatases (PTPs).
• Previous studies revealed loop motions within PTP active sites, influencing catalysis and allostery.

Purpose of the Study:

• To investigate the conformational dynamics and catalytic mechanisms of the thermophilic PTP, Sulfolobus solfataricus PTP (SsoPTP).
• To elucidate the roles of specific loops and residues in SsoPTP's enzymatic activity.

Main Methods:

• Nuclear magnetic resonance (NMR) spectroscopy
• Computational analyses
• Mutagenesis studies
• Kinetic assays
• Isotope effect measurements
• High-resolution X-ray crystallography with vanadate.

Main Results:

• SsoPTP exhibits coupled motions in its acid loop, P-loop, and Q-loop, a novel observation in PTPs.
• Mutagenesis and kinetic data identify E40 as an alternate general acid catalyst.
• X-ray structure reveals the role of active site arginine R102 in catalysis.

Conclusions:

• The coordinated dynamics of SsoPTP's functional loops suggest coupled motions are essential for catalysis.
• The identification of an unconventional alternate general acid (E40) expands our understanding of PTP catalytic strategies.
• Catalytically active conformations may exist in solution that are not captured by static crystal structures.