1kgu: Difference between revisions

Revision as of 14:34, 21 February 2008

THREE DIMENSIONAL STRUCTURE ANALYSIS OF THE R337A VARIANT OF HUMAN PANCREATIC ALPHA-AMYLASE

OverviewOverview

Human pancreatic alpha-amylase (HPA) is a member of the alpha-amylase family involved in the degradation of starch. Some members of this family, including HPA, require chloride for maximal activity. To determine the mechanism of chloride activation, a series of mutants (R195A, R195Q, N298S, R337A, and R337Q) were made in which residues in the chloride ion binding site were replaced. Mutations in this binding site were found to severely affect the ability of HPA to bind chloride ions with no binding detected for the R195 and R337 mutant enzymes. X-ray crystallographic analysis revealed that these mutations did not result in significant structural changes. However, the introduction of these mutations did alter the kinetic properties of the enzyme. Mutations to residue R195 resulted in a 20-450-fold decrease in the activity of the enzyme toward starch and shifted the pH optimum to a more basic pH. Interestingly, replacement of R337 with a nonbasic amino acid resulted in an alpha-amylase that no longer required chloride for catalysis and has a pH profile similar to that of wild-type HPA. In contrast, a mutation at residue N298 resulted in an enzyme that had much lower binding affinity for chloride but still required chloride for maximal activity. We propose that the chloride is required to increase the pK(a) of the acid/base catalyst, E233, which would otherwise be lower due to the presence of R337, a positively charged residue.

About this StructureAbout this Structure

1KGU is a Single protein structure of sequence from Homo sapiens with as ligand. Active as Alpha-amylase, with EC number 3.2.1.1 Full crystallographic information is available from OCA.

ReferenceReference

Probing the role of the chloride ion in the mechanism of human pancreatic alpha-amylase., Numao S, Maurus R, Sidhu G, Wang Y, Overall CM, Brayer GD, Withers SG, Biochemistry. 2002 Jan 8;41(1):215-25. PMID:11772019

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 ==Overview==
-Human pancreatic alpha-amylase (HPA) is a member of the alpha-amylase, family involved in the degradation of starch. Some members of this family, including HPA, require chloride for maximal activity. To determine the, mechanism of chloride activation, a series of mutants (R195A, R195Q, N298S, R337A, and R337Q) were made in which residues in the chloride ion, binding site were replaced. Mutations in this binding site were found to, severely affect the ability of HPA to bind chloride ions with no binding, detected for the R195 and R337 mutant enzymes. X-ray crystallographic, analysis revealed that these mutations did not result in significant, structural changes. However, the introduction of these mutations did alter, the kinetic properties of the enzyme. Mutations to residue R195 resulted, in a 20-450-fold decrease in the activity of the enzyme toward starch and, shifted the pH optimum to a more basic pH. Interestingly, replacement of, R337 with a nonbasic amino acid resulted in an alpha-amylase that no, longer required chloride for catalysis and has a pH profile similar to, that of wild-type HPA. In contrast, a mutation at residue N298 resulted in, an enzyme that had much lower binding affinity for chloride but still, required chloride for maximal activity. We propose that the chloride is, required to increase the pK(a) of the acid/base catalyst, E233, which, would otherwise be lower due to the presence of R337, a positively charged, residue.
+Human pancreatic alpha-amylase (HPA) is a member of the alpha-amylase family involved in the degradation of starch. Some members of this family, including HPA, require chloride for maximal activity. To determine the mechanism of chloride activation, a series of mutants (R195A, R195Q, N298S, R337A, and R337Q) were made in which residues in the chloride ion binding site were replaced. Mutations in this binding site were found to severely affect the ability of HPA to bind chloride ions with no binding detected for the R195 and R337 mutant enzymes. X-ray crystallographic analysis revealed that these mutations did not result in significant structural changes. However, the introduction of these mutations did alter the kinetic properties of the enzyme. Mutations to residue R195 resulted in a 20-450-fold decrease in the activity of the enzyme toward starch and shifted the pH optimum to a more basic pH. Interestingly, replacement of R337 with a nonbasic amino acid resulted in an alpha-amylase that no longer required chloride for catalysis and has a pH profile similar to that of wild-type HPA. In contrast, a mutation at residue N298 resulted in an enzyme that had much lower binding affinity for chloride but still required chloride for maximal activity. We propose that the chloride is required to increase the pK(a) of the acid/base catalyst, E233, which would otherwise be lower due to the presence of R337, a positively charged residue.
 ==About this Structure==
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 [[Category: Homo sapiens]]
 [[Category: Single protein]]
-[[Category: Brayer, G.D.]]
+[[Category: Brayer, G D.]]
 [[Category: Maurus, R.]]
 [[Category: Numao, S.]]
-[[Category: Overall, C.M.]]
+[[Category: Overall, C M.]]
 [[Category: Sidhu, G.]]
 [[Category: Wang, Y.]]
-[[Category: Withers, S.G.]]
+[[Category: Withers, S G.]]
 [[Category: CA]]
 [[Category: alpha-amylase]]
@@ Line 31: / Line 31: @@
 [[Category: pichia pastoris]]
-''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri Feb 15 16:13:23 2008''
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 13:33:59 2008''