Morphology of the procarboxypeptidase A-S6 complex. A solution X-ray scattering study

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Bovine pancreatic procarboxypeptidase A is secreted as a non-covalent ternary complex (pro CPA-S6).
• Dimethylmaleylation allows dissociation into free native subunits.
• Specific binary complexes (pro CPA-S6 subunits I-II, I-III) form due to high-affinity interactions.

Purpose of the Study:

• To investigate the morphology of the pro CPA-S6 ternary complex using solution X-ray scattering.
• To understand the functional significance of the subunit association.
• To construct a model for the interaction between carboxypeptidase A and its activation peptide.

Main Methods:

• Solution X-ray scattering was employed to study the morphology of the ternary complex and its components.
• Radii of gyration were calculated for all molecular species.
• Experimental data were interpreted using compact object models and anisotropy calculations.

Main Results:

• All molecular species (ternary complex, binary complexes, free subunits) were characterized as globular particles.
• Moderate anisotropy suggested simple geometric shapes for the components.
• Inter-center distances indicated close packing, with complex I-III being more open than I-II.

Conclusions:

• The study provides insights into the quaternary structure of bovine pancreatic procarboxypeptidase A.
• The results suggest close spatial arrangements of subunits within the complex.
• A model for carboxypeptidase A and its activation peptide interaction was proposed based on structural data.