title: NMR studies on structure and dynamics of the monomeric derivative of BS-RNase: new insights for 3D domain swapping.
abstract: Three-dimensional domain swapping is a common phenomenon in pancreatic-like ribonucleases. In the aggregated state, these proteins acquire new biological functions, including selective cytotoxicity against tumour cells. RNase A is able to dislocate both N- and C-termini, but usually this process requires denaturing conditions. In contrast, bovine seminal ribonuclease (BS-RNase), which is a homo-dimeric protein sharing 80% of sequence identity with RNase A, occurs natively as a mixture of swapped and unswapped isoforms. The presence of two disulfides bridging the subunits, indeed, ensures a dimeric structure also to the unswapped molecule. In vitro, the two BS-RNase isoforms interconvert under physiological conditions. Since the tendency to swap is often related to the instability of the monomeric proteins, in these paper we have analysed in detail the stability in solution of the monomeric derivative of BS-RNase (mBS) by a combination of NMR studies and Molecular Dynamics Simulations. The refinement of NMR structure and relaxation data indicate a close similarity with RNase A, without any evidence of aggregation or partial opening. The high compactness of mBS structure is confirmed also by H/D exchange, urea denaturation, and TEMPOL mapping of the protein surface. The present extensive structural and dynamic investigation of (monomeric) mBS did not show any experimental evidence that could explain the known differences in swapping between BS-RNase and RNase A. Hence, we conclude that the swapping in BS-RNase must be influenced by the distinct features of the dimers, suggesting a prominent role for the interchain disulfide bridges.
authors.affiliation: Dipartimento di Scienze Biologiche ed Ambientali, Università del Sannio, Benevento, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Spadaccini
authors.forename: Carmine
authors.initials: C
authors.lastname: Ercole
authors.forename: Maria A
authors.initials: MA
authors.lastname: Gentile
authors.forename: Domenico
authors.initials: D
authors.lastname: Sanfelice
authors.forename: Rolf
authors.initials: R
authors.lastname: Boelens
authors.forename: Rainer
authors.initials: R
authors.lastname: Wechselberger
authors.forename: Gyula
authors.initials: G
authors.lastname: Batta
authors.forename: Andrea
authors.initials: A
authors.lastname: Bernini
authors.forename: Neri
authors.initials: N
authors.lastname: Niccolai
authors.forename: Delia
authors.initials: D
authors.lastname: Picone
mesh_terms: D000818:Animals; D002417:Cattle; D003497:Cyclic N-Oxides / Q000494:pharmacology; D041961:Deuterium Exchange Measurement; D004722:Endoribonucleases / Q000737:chemistry* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D056004:Molecular Dynamics Simulation; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding / Q000187:drug effects; D013113:Spin Labels; D013499:Surface Properties / Q000187:drug effects; D013816:Thermodynamics; D014508:Urea / Q000494:pharmacology
chemical_list: D003497:Cyclic N-Oxides; D013113:Spin Labels; D014508:Urea; D004722:Endoribonucleases; C032523:ribonuclease SPL; C001803:tempol