1KGX

Three Dimensional Structure Analysis of the R195Q Variant of Human Pancreatic Alpha Amylase


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2 Å
  • R-Value Work: 0.197 

wwPDB Validation 3D Report Full Report


This is version 1.2 of the entry. See complete history

Literature

Probing the role of the chloride ion in the mechanism of human pancreatic alpha-amylase.

Numao, S.Maurus, R.Sidhu, G.Wang, Y.Overall, C.M.Brayer, G.D.Withers, S.G.

(2002) Biochemistry 41: 215-225

  • Primary Citation of Related Structures:  1KB3, 1KGU, 1KGW

  • PubMed Abstract: 
  • 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, ...

    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.


    Organizational Affiliation

    Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.




Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
ALPHA-AMYLASE, PANCREATIC
A
496Homo sapiensGene Names: AMY2A
EC: 3.2.1.1
Find proteins for P04746 (Homo sapiens)
Go to Gene View: AMY2A
Go to UniProtKB:  P04746
Small Molecules
Ligands 2 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
CA
Query on CA

Download SDF File 
Download CCD File 
A
CALCIUM ION
Ca
BHPQYMZQTOCNFJ-UHFFFAOYSA-N
 Ligand Interaction
NAG
Query on NAG

Download SDF File 
Download CCD File 
A
N-ACETYL-D-GLUCOSAMINE
C8 H15 N O6
OVRNDRQMDRJTHS-FMDGEEDCSA-N
 Ligand Interaction
Modified Residues  1 Unique
IDChainsTypeFormula2D DiagramParent
PCA
Query on PCA
A
L-PEPTIDE LINKINGC5 H7 N O3GLU
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2 Å
  • R-Value Work: 0.197 
  • Space Group: P 21 21 21
Unit Cell:
Length (Å)Angle (°)
a = 53.081α = 90.00
b = 69.027β = 90.00
c = 131.827γ = 90.00
Software Package:
Software NamePurpose
DENZOdata reduction
X-PLORphasing
X-PLORmodel building
X-PLORrefinement
SCALEPACKdata scaling

Structure Validation

View Full Validation Report or Ramachandran Plots



Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2002-01-16
    Type: Initial release
  • Version 1.1: 2008-04-27
    Type: Version format compliance
  • Version 1.2: 2011-07-13
    Type: Non-polymer description, Version format compliance