1H6M: Covalent Glycosyl-enzyme Intermediate of HEN EGG White Lysozyme

Citation:
Abstract
Hen egg-white lysozyme (HEWL) was the first enzyme to have its three-dimensional structure determined by X-ray diffraction techniques. A catalytic mechanism, featuring a long-lived oxocarbenium-ion intermediate, was proposed on the basis of model-building studies. The 'Phillips' mechanism is widely held as the paradigm for the catalytic mechanism of beta-glycosidases that cleave glycosidic linkages with net retention of configuration of the anomeric centre. Studies with other retaining beta-glycosidases, however, provide strong evidence pointing to a common mechanism for these enzymes that involves a covalent glycosyl-enzyme intermediate, as previously postulated. Here we show, in three different cases using electrospray ionization mass spectrometry, a catalytically competent covalent glycosyl-enzyme intermediate during the catalytic cycle of HEWL. We also show the three-dimensional structure of this intermediate as determined by X-ray diffraction. We formulate a general catalytic mechanism for all retaining beta-glycosidases that includes substrate distortion, formation of a covalent intermediate, and the electrophilic migration of C1 along the reaction coordinate.
PDB ID: 1H6MDownload
MMDB ID: 72236
PDB Deposition Date: 2001/6/19
Updated in MMDB: 2011/05
Experimental Method:
x-ray diffraction
Resolution: 1.64  Å
Source Organism:
Similar Structures:
Biological Unit for 1H6M: monomeric; determined by author and by software (PISA)
Molecular Components in 1H6M
Label Count Molecule
Protein (1 molecule)
1
Lysozyme C(Gene symbol: LYZ)
Molecule annotation
Chemicals (3 molecules)
1
1
2
1
3
1
* Click molecule labels to explore molecular sequence information.

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