2RLN: THERMODYNAMIC AND STRUCTURAL CONSEQUENCES OF CHANGING A SULPHUR ATOM TO A METHYLENE GROUP IN THE M13NLE MUTATION IN RIBONUCLEASE S

Citation:
Abstract
Two fragments of pancreatic ribonuclease A, a truncated version of S-peptide (residues 1-15) and S-protein (residues 21-124), combine to give a catalytically active complex. We have substituted the wild-type residue at position 13, methionine (Met), with norleucine (Nle), where the only covalent change is the replacement of the sulfur atom with a methylene group. The thermodynamic parameters associated with the binding of this variant to S-protein, determined by titration calorimetry in the temperature range 10-40 degrees C, are reported and compared to values previously reported [Varadarajan, R., Connelly, P. R., Sturtevant, J. M., & Richards, F. M. (1992) Biochemistry 31, 1421-1426] for other position 13 analogs. The differences in the free energy and enthalpy of binding between the Met and Nle peptides are 0.6 and 7.9 kcal/mol at 25 degrees C, respectively. These differences are slightly larger than, but comparable to, the differences in the values for the Met/Ile and Met/Leu pairs. The structure of the mutant complex was determined to 1.85 A resolution and refined to an R-factor of 17.4%. The structures of mutant and wild-type complexes are practically identical although the Nle side chain has a significantly higher average B-factor than the corresponding Met side chain. In contrast, the B-factors of the atoms of the cage of residues surrounding position 13 are all somewhat lower in the Nle variant than the Met wild-type.(ABSTRACT TRUNCATED AT 250 WORDS)
PDB ID: 2RLNDownload
MMDB ID: 156863
PDB Deposition Date: 1994/7/11
Updated in MMDB: 2017/12
Experimental Method:
x-ray diffraction
Resolution: 1.85  Å
Source Organism:
Bos taurus
Similar Structures:
Biological Unit for 2RLN: dimeric; determined by author and by software (PISA)
Molecular Components in 2RLN
Label Count Molecule
Proteins (2 molecules)
1
Ribonuclease
Molecule annotation
1
Ribonuclease S (S-protein)
Molecule annotation
Chemical (1 molecule)
1
1
* Click molecule labels to explore molecular sequence information.

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