1h6m: Difference between revisions
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==Overview== | ==Overview== | ||
Hen egg-white lysozyme (HEWL) was the first enzyme to have its | 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. | ||
==About this Structure== | ==About this Structure== | ||
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[[Category: Lysozyme]] | [[Category: Lysozyme]] | ||
[[Category: Single protein]] | [[Category: Single protein]] | ||
[[Category: Davies, G | [[Category: Davies, G J.]] | ||
[[Category: Laine, R.]] | [[Category: Laine, R.]] | ||
[[Category: Vocadlo, D | [[Category: Vocadlo, D J.]] | ||
[[Category: Withers, S | [[Category: Withers, S G.]] | ||
[[Category: NA]] | [[Category: NA]] | ||
[[Category: covalent intermediate]] | [[Category: covalent intermediate]] | ||
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[[Category: mechanism]] | [[Category: mechanism]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 12:57:59 2008'' | ||
Revision as of 13:57, 21 February 2008
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COVALENT GLYCOSYL-ENZYME INTERMEDIATE OF HEN EGG WHITE LYSOZYME
OverviewOverview
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.
About this StructureAbout this Structure
1H6M is a Single protein structure of sequence from Gallus gallus with as ligand. Active as Lysozyme, with EC number 3.2.1.17 Known structural/functional Sites: , and . Full crystallographic information is available from OCA.
ReferenceReference
Catalysis by hen egg-white lysozyme proceeds via a covalent intermediate., Vocadlo DJ, Davies GJ, Laine R, Withers SG, Nature. 2001 Aug 23;412(6849):835-8. PMID:11518970
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