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Structural basis for dimerization, catalytic regulation, and substrate selectivity in S9D proteases.

Jacqueline J Ehrlich1, Pratyush Routray2, Louis Enns1

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Summary

Researchers reveal the structure of a plant S9D protease, chloroplast glutamyl endopeptidase (CGEP). This protease uses a unique hinge-loop gate mechanism for regulation and shows a strong preference for glutamate, advancing protease understanding.

Keywords:
S9 protease familychloroplast proteostasiscryo-electron microscopyglutamyl endopeptidase

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Area of Science:

  • Proteases
  • Structural Biology
  • Plant Biochemistry

Background:

  • S9 proteases are vital for protein processing across life.
  • The structural and mechanistic basis of S9D subfamily proteases remained largely unknown.

Purpose of the Study:

  • To determine the high-resolution cryo-EM structures of an S9D protease, chloroplast glutamyl endopeptidase (CGEP).
  • To elucidate the structural and mechanistic basis of CGEP activity and substrate specificity.

Main Methods:

  • High-resolution cryo-electron microscopy (cryo-EM) of CGEP.
  • Protein expression in plants and bacteria.
  • Structural analysis and mutagenesis studies.

Main Results:

  • CGEP forms a stable dimer via hydrophobic and interdomain β-sheet interactions.
  • A hinge loop acts as a steric gate, regulating substrate access and catalytic activity.
  • CGEP maintains an intact catalytic triad, regulated by hinge-loop gating, not catalytic disruption.
  • A conserved pocket in the hinge loop explains CGEP's strong preference for glutamate.

Conclusions:

  • This study uncovers a unique regulatory mechanism for S9D proteases involving hinge-loop gating.
  • The findings provide a structural framework for understanding CGEP's substrate selectivity and dimerization.
  • Advances understanding of protease diversity and opens avenues for protease engineering.