Amylase: Difference between revisions

Shown in Figure 1, is the structure of the themostable α-amylase of ''Bacillus stearothermophilus'' (BSTA)<ref name="Main"/>. BSTA comprises of a single polypeptide chain. This chain is folded into three domains: A, B and C. These domains are generally found on all α-amylase enzymes. The <scene name='Sandbox_182/Domain_aa/1'>A domain </scene>constitutes the core structure, with a (β/α)bar rel.The <scene name='Sandbox_182/Domain_a/1'> B domain</scene> consists of a sheet of four anti-parallel β-strands with a pair of anti-parallel  β-strands. Long loops are observed between the β-strands.  Located within the B domain is the <scene name='Sandbox_182/Trio/1'>binding site</scene> for Ca²⁺-Na⁺-Ca²⁺. <scene name='Sandbox_182/Domain_c/1'>Domain C </scene>consisting of eight β-strands assembled into a globular unit forming a Greek key motif.  It also holds the <scene name='Sandbox_182/Caiii/1'>third </scene>Ca²⁺ binding site in association with domain A. Positioned on the C-terminal side of the β-strands of the (β/α)barrel in domain A is the active site.  The catalytic residues involved for the BSTA active site are Asp234, Glu264, and Asp331. The residues are identical to other α-amylases, yet there are positional differences which reflect the flexible nature of catalytic resides.

<scene name='Sandbox_182/Trio/1'>CaII and CaI with Na</scene> found in the interior of domain B and <scene name='Sandbox_182/Caiii/1'>CaIII </scene>at the interface of domain A and C, constitute the metal ion binding sites. All α-amylases contain one strongly conserved Ca²⁺ ion for structural intregity and enzymatic activity.<ref name="chloride">PMID: 12021442</ref> CaI is consistent in α-amylases, however there are structural differences between the linear trio of CaI, CaII and Na in other enzymes. CaIII acts as a bridge between two loops, one from Aα6 of domain A, and one between Cβ1 and Cβ2 of domain C.

  A family of chloride dependent enzymes including salivary and pancreatic α-amylase, require the binding of a chloride ion to be allosterically activated.<ref name="chloride"/> The function of the chloride ion still remains uncertain. No relationship has been observed between the anion binding affinity and its activity, indicating the complexity between the binding parameters and mechanism it activates. Studies have shown that nitrite and nitrate ions with pancreatic α-amylase, fit within the chloride binding site thus making all the necessary hydrogen bonds, and enhancing the relative activity by a 5-fold.<ref>PMID: 18284212</ref>