1WCQ: Mutagenesis Of The Nucleophilic Tyrosine In A Bacterial Sialidase To Phenylalanine

Mutants of the Micromonospora viridifaciens sialidase, Y370E and Y370F, are catalytically active retaining enzymes that operate by different mechanisms. Previous substitutions with smaller amino acids, including Y370D, yielded inverting sialidases. At least one water molecule can fit into the active-site cavity of this mutant and act as a nucleophile from the face opposite the leaving group (Biochemistry 2003, 42, 12 682). Thus, addition of a CH(2) unit (Asp versus Glu) changes the mechanism from inversion back to retention of configuration. Based on Bronsted beta(lg) values, it is proposed that the Y370E mutant reacts by a double-displacement mechanism (beta(lg) on k(cat)/K(m) -0.36+/-0.04) with Glu370 acting as the nucleophile. However, the Y370F mutant (beta(lg) on k(cat)/K(m) -0.79+/-0.12) reacts via a dissociative transition state. The crystal structure of the Y370F mutant complexed with 2-deoxy-2,3-dehydro-N-acetylneuraminic acid shows no significant active-site perturbation relative to the wild-type enzyme.
PDB ID: 1WCQDownload
MMDB ID: 35456
PDB Deposition Date: 2004/11/19
Updated in MMDB: 2005/11
Experimental Method:
x-ray diffraction
Resolution: 2.1  Å
Source Organism:
Similar Structures:
Biological Unit for 1WCQ: monomeric; determined by author and by software (PQS)
Molecular Components in 1WCQ
Label Count Molecule
Protein (1 molecule)
Molecule annotation
Chemicals (4 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB