Bovine seminal RNase, a homodimeric enzyme joined covalently by two interchain disulfide bonds, is an equil. mixt. of two conformational isomers, M´M and M=M. The major form, M´M, whose crystal structure has been previously detd. at 1.9 .ANG. resoln., presents the swapping of the N-terminal segments (residues 1-15) and composite active sites formed by residues of different chains. The three-dimensional domain swapping does not occur in the M=M form. The different fold of each N-terminal tail is directed by the hinge loop (residue 16-22) connecting the swapping domain to the body of the protein. Redn. and alkylation of interchain disulfide bridges produce a monomeric deriv. and a noncovalent swapped dimer, which are both active. The free and nucleotide-bound forms of the monomer have been crystd. at an alk. pH and refined at 1.45 and 1.65 .ANG. resoln., resp. In both cases, the N-terminal fragment is folded on the main body of the protein to produce an intact active site and a chain architecture very similar to that of bovine pancreatic RNase. In this new fold of the seminal chain, the hinge loop is disordered. Despite the difference between the tertiary structure of the monomer and that of the chains in the M´M form, the active sites of the two enzymes are virtually indistinguishable. Furthermore, the structure of the liganded enzyme represents the first example of a RNase complex studied at an alk. pH and provides new information on the binding of a nucleotide when the catalytic histidines are deprotonated.
The unswapped chain of bovine seminal ribonuclease: Crystal structure of the free and liganded monomeric derivative.
2003
Abstract
Bovine seminal RNase, a homodimeric enzyme joined covalently by two interchain disulfide bonds, is an equil. mixt. of two conformational isomers, M´M and M=M. The major form, M´M, whose crystal structure has been previously detd. at 1.9 .ANG. resoln., presents the swapping of the N-terminal segments (residues 1-15) and composite active sites formed by residues of different chains. The three-dimensional domain swapping does not occur in the M=M form. The different fold of each N-terminal tail is directed by the hinge loop (residue 16-22) connecting the swapping domain to the body of the protein. Redn. and alkylation of interchain disulfide bridges produce a monomeric deriv. and a noncovalent swapped dimer, which are both active. The free and nucleotide-bound forms of the monomer have been crystd. at an alk. pH and refined at 1.45 and 1.65 .ANG. resoln., resp. In both cases, the N-terminal fragment is folded on the main body of the protein to produce an intact active site and a chain architecture very similar to that of bovine pancreatic RNase. In this new fold of the seminal chain, the hinge loop is disordered. Despite the difference between the tertiary structure of the monomer and that of the chains in the M´M form, the active sites of the two enzymes are virtually indistinguishable. Furthermore, the structure of the liganded enzyme represents the first example of a RNase complex studied at an alk. pH and provides new information on the binding of a nucleotide when the catalytic histidines are deprotonated.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
