3BCP

Crystal Structure of The Swapped non covalent form of P19A/L28Q/N67D BS-RNase

Summary for 3BCP

• Entry DOI: 10.2210/pdb3bcp/pdb
• Related: 3BCM 3BCO
• Descriptor: Seminal ribonuclease (2 entities in total)
• Functional Keywords: domain swapping, bovine seminal ribonuclease, non covalent dimer, antitumor activity, allosteric enzyme, endonuclease, hydrolase, secreted
• Biological source: Bos taurus (cattle)
• Cellular location: Secreted: P00669
• Total number of polymer chains: 4
• Total formula weight: 54946.64

Authors

Merlino, A.,Ercole, C.,Picone, D.,Pizzo, E.,Mazzarella, L.,Sica, F. (deposition date: 2007-11-13, release date: 2008-02-12, Last modification date: 2023-11-01)

Primary citation

Merlino, A.,Ercole, C.,Picone, D.,Pizzo, E.,Mazzarella, L.,Sica, F.
The buried diversity of bovine seminal ribonuclease: shape and cytotoxicity of the swapped non-covalent form of the enzyme
J.Mol.Biol., 376:427-437, 2008

PubMed Abstract: Bovine seminal ribonuclease exists in the native state as an equilibrium mixture of a swapped and an unswapped dimer. The molecular envelope and the exposed surface of the two isomers are practically indistinguishable and their diversity is almost completely buried in the interior of the protein. Surprisingly, the cytotoxic and antitumor activity of the enzyme is a peculiar property of the swapped dimer. This buried diversity comes into light in the reducing environment of the cytosol, where the unswapped dimer dissociates into monomers, whereas the swapped one generates a metastable dimeric form (NCD-BS) with a quaternary assembly that allows the molecule to escape the protein inhibitor of ribonucleases. The stability of this quaternary shape was mainly attributed to the combined presence of Pro19 and Leu28. We have prepared and fully characterized by X-ray diffraction the double mutant P19A/L28Q (PALQ) of the seminal enzyme. While the swapped and unswapped forms of the mutant have structures very similar to that of the corresponding wild-type forms, the non-covalent form (NCD-PALQ) adopts an opened quaternary structure, different from that of NCD-BS. Moreover, model building clearly indicates that NCD-PALQ can be easily sequestered by the protein inhibitor. In agreement with these results, cytotoxic assays have revealed that PALQ has limited activity, whereas the single mutants P19A and L28Q display cytotoxic activity against malignant cells almost as large as the wild-type enzyme. The significant increase in the antitumor activity, brought about by the substitution of just two residues in going from the double mutant to the wild-type enzyme, suggests a new strategy to improve this important biological property by strengthening the interface that stabilizes the quaternary structure of NCD-BS.

PubMed: 18164315
DOI: 10.1016/j.jmb.2007.11.008

Experimental method

X-RAY DIFFRACTION (2.57 Å)