Dynamical structure of carboxypeptidase A.

Area of Science:

• Biochemistry and Structural Biology
• Computational Biophysics

Background:

• Carboxypeptidase A (EC 3.4.12.2) is a zinc metalloenzyme crucial for protein hydrolysis.
• Understanding its structural dynamics is key to elucidating its catalytic mechanism.

Purpose of the Study:

• To investigate the structural fluctuations of the apoenzyme form of carboxypeptidase A.
• To correlate protein dynamics with functional sites, including substrate recognition and the active site.

Main Methods:

• Molecular dynamics simulations at 277 K using refined X-ray crystallographic coordinates.
• Analysis of atomic displacements and root-mean-square (r.m.s.) fluctuations over a 48 picosecond trajectory.
• Evaluation of secondary structure preservation and active site residue dynamics.

Main Results:

• High-amplitude motion observed in residues at intermolecular contact sites.
• Preservation of alpha-helices and beta-strands, with notable unwinding at a C-terminal contact site.
• A stable core of secondary structure near the active site was identified.
• The absence of the zinc ion did not significantly alter active site stereochemistry.
• Residues involved in substrate binding and scissile bond cleavage showed low motion, while distal recognition sites exhibited higher fluctuations.

Conclusions:

• Protein dynamics are linked to functional roles, with conserved motion in the active site core.
• Differential motional fluctuations in substrate recognition sites are essential for substrate hydrolysis.
• The apoenzyme's dynamics provide insights into substrate binding and catalytic mechanisms.