1xgz
From Proteopedia
(New page: 200px<br /> <applet load="1xgz" size="450" color="white" frame="true" align="right" spinBox="true" caption="1xgz, resolution 2.0Å" /> '''Structure of the N29...) |
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caption="1xgz, resolution 2.0Å" /> | caption="1xgz, resolution 2.0Å" /> | ||
'''Structure of the N298S variant of human pancreatic alpha-amylase'''<br /> | '''Structure of the N298S variant of human pancreatic alpha-amylase'''<br /> | ||
==Overview== | ==Overview== | ||
| - | The mechanism of allosteric activation of alpha-amylase by chloride has | + | The mechanism of allosteric activation of alpha-amylase by chloride has been studied through structural and kinetic experiments focusing on the chloride-dependent N298S variant of human pancreatic alpha-amylase (HPA) and a chloride-independent TAKA-amylase. Kinetic analysis of the HPA variant clearly demonstrates the pronounced activating effect of chloride ion binding on reaction rates and its effect on the pH-dependence of catalysis. Structural alterations observed in the N298S variant upon chloride ion binding suggest that the chloride ion plays a variety of roles that serve to promote catalysis. One of these is having a strong influence on the positioning of the acid/base catalyst residue E233. Absence of chloride ion results in multiple conformations for this residue and unexpected enzymatic products. Chloride ion and N298 also appear to stabilize a helical region of polypeptide chain from which projects the flexible substrate binding loop unique to chloride-dependent alpha-amylases. This structural feature also serves to properly orient the catalytically essential residue D300. Comparative analyses show that the chloride-independent alpha-amylases compensate for the absence of bound chloride by substituting a hydrophobic core, altering the manner in which substrate interactions are made and shifting the placement of N298. These evolutionary differences presumably arise in response to alternative operating environments or the advantage gained in a particular product profile. Attempts to engineer chloride-dependence into the chloride-independent TAKA-amylase point out the complexity of this system, and the fact that a multitude of factors play a role in binding chloride ion in the chloride-dependent alpha-amylases. |
==About this Structure== | ==About this Structure== | ||
| - | 1XGZ is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] with NAG and CA as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Alpha-amylase Alpha-amylase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.1.1 3.2.1.1] Full crystallographic information is available from [http:// | + | 1XGZ is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] with <scene name='pdbligand=NAG:'>NAG</scene> and <scene name='pdbligand=CA:'>CA</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Alpha-amylase Alpha-amylase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.1.1 3.2.1.1] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1XGZ OCA]. |
==Reference== | ==Reference== | ||
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[[Category: Single protein]] | [[Category: Single protein]] | ||
[[Category: Begum, A.]] | [[Category: Begum, A.]] | ||
| - | [[Category: Brayer, G | + | [[Category: Brayer, G D.]] |
| - | [[Category: Kuo, H | + | [[Category: Kuo, H H.]] |
[[Category: Maurus, R.]] | [[Category: Maurus, R.]] | ||
[[Category: Numao, S.]] | [[Category: Numao, S.]] | ||
| - | [[Category: Overall, C | + | [[Category: Overall, C M.]] |
[[Category: Racaza, A.]] | [[Category: Racaza, A.]] | ||
| - | [[Category: Withers, S | + | [[Category: Withers, S G.]] |
[[Category: CA]] | [[Category: CA]] | ||
[[Category: NAG]] | [[Category: NAG]] | ||
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[[Category: inhibitor]] | [[Category: inhibitor]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 15:54:44 2008'' |
Revision as of 13:54, 21 February 2008
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Structure of the N298S variant of human pancreatic alpha-amylase
Overview
The mechanism of allosteric activation of alpha-amylase by chloride has been studied through structural and kinetic experiments focusing on the chloride-dependent N298S variant of human pancreatic alpha-amylase (HPA) and a chloride-independent TAKA-amylase. Kinetic analysis of the HPA variant clearly demonstrates the pronounced activating effect of chloride ion binding on reaction rates and its effect on the pH-dependence of catalysis. Structural alterations observed in the N298S variant upon chloride ion binding suggest that the chloride ion plays a variety of roles that serve to promote catalysis. One of these is having a strong influence on the positioning of the acid/base catalyst residue E233. Absence of chloride ion results in multiple conformations for this residue and unexpected enzymatic products. Chloride ion and N298 also appear to stabilize a helical region of polypeptide chain from which projects the flexible substrate binding loop unique to chloride-dependent alpha-amylases. This structural feature also serves to properly orient the catalytically essential residue D300. Comparative analyses show that the chloride-independent alpha-amylases compensate for the absence of bound chloride by substituting a hydrophobic core, altering the manner in which substrate interactions are made and shifting the placement of N298. These evolutionary differences presumably arise in response to alternative operating environments or the advantage gained in a particular product profile. Attempts to engineer chloride-dependence into the chloride-independent TAKA-amylase point out the complexity of this system, and the fact that a multitude of factors play a role in binding chloride ion in the chloride-dependent alpha-amylases.
About this Structure
1XGZ is a Single protein structure of sequence from Homo sapiens with and as ligands. Active as Alpha-amylase, with EC number 3.2.1.1 Full crystallographic information is available from OCA.
Reference
Structural and mechanistic studies of chloride induced activation of human pancreatic alpha-amylase., Maurus R, Begum A, Kuo HH, Racaza A, Numao S, Andersen C, Tams JW, Vind J, Overall CM, Withers SG, Brayer GD, Protein Sci. 2005 Mar;14(3):743-55. PMID:15722449
Page seeded by OCA on Thu Feb 21 15:54:44 2008
Categories: Alpha-amylase | Homo sapiens | Single protein | Begum, A. | Brayer, G D. | Kuo, H H. | Maurus, R. | Numao, S. | Overall, C M. | Racaza, A. | Withers, S G. | CA | NAG | Acarbose | Amylase | Chloride | Enzyme | Inhibitor
