4K1U: Crystal Structure Of Delta5-3-ketosteroid Isomerase Containing Y16f And Y32f Mutations

Proteins have evolved to compensate for detrimental mutations. However, compensatory mechanisms for protein defects are not well understood. Using ketosteroid isomerase (KSI), we investigated how second-site mutations could recover defective mutant function and stability. Previous results revealed that the Y30F mutation rescued the Y14F, Y55F and Y14F/Y55F mutants by increasing the catalytic activity by 23-, 3- and 1.3-fold, respectively, and the Y55F mutant by increasing the stability by 3.3 kcal/mol. To better understand these observations, we systematically investigated detailed structural and thermodynamic effects of the Y30F mutation on these mutants. Crystal structures of the Y14F/Y30F and Y14F/Y55F mutants were solved at 2.0 and 1.8 previoulsy solved structures of wild-type and other mutant KSIs. Structural analyses revealed that the Y30F mutation partially restored the active-site cleft of these mutant KSIs. The Y30F mutation also increased Y14F and Y14F/Y55F mutant stability by 3.2 and 4.3 kcal/mol, respectively, and the melting temperatures of the Y14F, Y55F and Y14F/Y55F mutants by 6.4 degrees C, 5.1 degrees C and 10.0 degrees C, respectively. Compensatory effects of the Y30F mutation on stability might be due to improved hydrophobic interactions because removal of a hydroxyl group from Tyr30 induced local compaction by neighboring residue movement and enhanced interactions with surrounding hydrophobic residues in the active site. Taken together, our results suggest that perturbed active-site geometry recovery and favorable hydrophobic interactions mediate the role of Y30F as a secondsite suppressor.
PDB ID: 4K1UDownload
MMDB ID: 112270
PDB Deposition Date: 2013/4/5
Updated in MMDB: 2013/09
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 4K1U: dimeric; determined by author and by software (PISA)
Molecular Components in 4K1U
Label Count Molecule
Proteins (2 molecules)
Steroid Delta-isomerase
Molecule annotation
* Click molecule labels to explore molecular sequence information.

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