The Actin-Binding Prolyl-Isomerase Par17 Sustains Its Substrate Selectivity by Interdomain Allostery

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Human peptidyl-prolyl-cis/trans isomerases (PPIases), Parvulin 14 (Par14) and Parvulin 17 (Par17), catalyze the isomerization of Xaa-Pro peptide bonds.
• These enzymes are critical for protein folding and cellular processes by modulating protein-substrate interactions.
• Despite sharing identical amino acid sequences, Par14 and Par17 exhibit distinct cellular functions.

Purpose of the Study:

• To elucidate the molecular basis for the differential cellular functions of Par14 and Par17.
• To investigate the role of the N-terminal extension unique to Par17 in substrate selectivity and cellular localization.
• To understand the mechanism by which Par17 interacts with its cellular targets, including actin.

Main Methods:

• Enzyme activity assays to measure PPIase kinetics.
• Nuclear Magnetic Resonance (NMR) spectroscopy to determine structural and dynamic properties.
• Mass spectrometry to identify protein interactions and modifications.
• Biochemical assays to assess substrate binding and selectivity.

Main Results:

• The 25-residue N-terminal extension of Par17 is responsible for its distinct substrate selectivity.
• This N-terminal extension operates through an intramolecular allosteric mechanism to regulate enzyme activity.
• Par17's N-terminal extension contains a motif that specifically binds to actin, suggesting a role in cytoskeletal regulation.
• Par14 lacks this N-terminal extension and exhibits different substrate preferences and cellular roles.

Conclusions:

• The N-terminal extension of Parvulin 17 is a key determinant of its unique substrate specificity and cellular function.
• Parvulin 17 utilizes an allosteric mechanism, modulated by its N-terminal extension, to achieve target selectivity.
• The interaction of Parvulin 17 with actin, mediated by its N-terminal extension, highlights its involvement in cytoskeletal dynamics.
• Understanding these differences is crucial for deciphering the specific roles of PPIases in cellular regulation and disease.