A growing number of pancreatic-type ribonucleases (RNases) present cytotoxic activity against malignant cells. The cytoxicity of these enzymes is related to their resistance to the ribonuclease protein inhibitor (RI). In particular, bovine seminal ribonuclease (BS-RNase) is toxic to tumor cells both in vitro and in vivo ...
A growing number of pancreatic-type ribonucleases (RNases) present cytotoxic activity against malignant cells. The cytoxicity of these enzymes is related to their resistance to the ribonuclease protein inhibitor (RI). In particular, bovine seminal ribonuclease (BS-RNase) is toxic to tumor cells both in vitro and in vivo. BS-RNase is a covalent dimer with two intersubunit disulfide bridges between Cys(31) of one chain and Cys(32) of the second and vice versa. The native enzyme is an equilibrium mixture of two isomers, MxM and M=M. In the former the two subunits swap their N-terminal helices. The cytotoxic action is a peculiar property of MxM. In the reducing environment of cytosol, M=M dissociates into monomers, which are strongly inhibited by RI, whereas MxM remains as a non-covalent dimer (NCD), which evades RI. We have solved the crystal structure of NCD, carboxyamidomethylated at residues Cys(31) and Cys(32) (NCD-CAM), in a complex with 2'-deoxycitidylyl(3'-5')-2'-deoxyadenosine. The molecule reveals a quaternary structural organization much closer to MxM than to other N-terminal-swapped non-covalent dimeric forms of RNases. Model building of the complexes between these non-covalent dimers and RI reveals that NCD-CAM is the only dimer equipped with a quaternary organization capable of interfering seriously with the binding of the inhibitor. Moreover, a detailed comparative structural analysis of the dimers has highlighted the residues, which are mostly important in driving the quaternary structure toward that found in NCD-CAM.
Related Citations:
Bovine seminal ribonuclease: structure at 1.9 A resolution Mazzarella, L., Capasso, S., Demasi, D., Dilorenzo, G., Mattia, C.A., Zagari, A. (1993) Acta Crystallogr D Biol Crystallogr 49: 389
Population shift vs induced fit: the case of bovine seminal ribonuclease swapping dimer Merlino, A., Vitagliano, L., Sica, F., Zagari, A., Mazzarella, L. (2004) Biopolymers 73: 689
Binding of a substrate analog to a domain swapping protein: X-ray structure of the complex of bovine seminal ribonuclease with uridylyl(2',5')adenosine Vitagliano, L., Adinolfi, S., Riccio, A., Sica, F., Zagari, A., Mazzarella, L. (1998) Protein Sci 7: 1691
A potential allosteric subsite generated by domain swapping in bovine seminal ribonuclease Vitagliano, L., Adinolfi, S., Sica, F., Merlino, A., Zagari, A., Mazzarella, L. (1999) J Mol Biol 293: 569
The unswapped chain of bovine seminal ribonuclease: Crystal structure of the free and liganded monomeric derivative Sica, F., Di Fiore, A., Zagari, A., Mazzarella, L. (2003) Proteins 52: 263
Crystal structure of the dimeric unswapped form of bovine seminal ribonuclease Berisio, R., Sica, F., De Lorenzo, C., Di Fiore, A., Piccoli, R., Zagari, A., Mazzarella, L. (2003) FEBS Lett 554: 105
Swapping structural determinants of ribonucleases: an energetic analysis of the hinge peptide 16-22 Mazzarella, L., Vitagliano, L., Zagari, A. (1995) Proc Natl Acad Sci U S A 92: 3799
Organizational Affiliation:
Dipartimento di Chimica, Università degli Studi di Napoli Federico II, Via Cynthia, 80126 Naples, Italy.
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