CIRCULAR-DICHROISM STUDY OF RIBONUCLEASE-A MUTANTS CONTAINING THE MINIMAL STRUCTURAL REQUIREMENTS FOR DIMERIZATION AND SWAPPING

Four residues Prol9, Leu28, Cys31 and Cys32 proved to be the minimal s tructural requirements in determining the dimeric structure and the N- terminal segment swapping of bovine seminal ribonuclease, BS-RNase. We analyzed the content of secondary and tertiary structures in RNase A, P-RNase A, PL-RNase A, MCAM-PLCC-RNase A and MCAM-BS-RNase, performin g near and far-UV CD spectra. It results that the five proteins have v ery similar native conformations. Thermal denaturation at pH 5.0 of th e proteins, studied by means of CD measurements, proved reversible and well represented by the two-state N double left right arrow D transit ion model. Thermodynamic data are discussed in the light of the struct ural information available for RNase A and BS-RNase. (C) 1998 Elsevier Science B.V. All rights reserved.