Sandbox Reserved 655: Difference between revisions
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The CBM facilitates the enzyme by binding the complex to the cellulose, thus maintaining the proximity of the enzyme and the substrate. It can also target areas of the cellulose that are specific to the enzyme complex. In addition, the CBM itself can disrupt the structure of the cellulose and thus expose the substrate more to the enzyme. The aromatic amino acid residues and planar architecture of the CBM binding sites are complementary to the hydrophobic sites of cellulose chains (hydrophobic 110 face) (Figure 3). This exposes the beta-D-glucopyranose rings in the chair conformation, which have their alpha and beta faces having either two or three axial hydrogens exposed and ring hydroxyl groups in the equatorial position, allowing the CBMs to bind efficiently (Nimlos, et al., 2007). The thermodynamic forces that drive this interaction is controversial, but most researchers postulate that it comes from the positive entropy when the water molecules are released from the protein and ligand (Boraston, et al., 2004). | The CBM facilitates the enzyme by binding the complex to the cellulose, thus maintaining the proximity of the enzyme and the substrate. It can also target areas of the cellulose that are specific to the enzyme complex. In addition, the CBM itself can disrupt the structure of the cellulose and thus expose the substrate more to the enzyme. The aromatic amino acid residues and planar architecture of the CBM binding sites are complementary to the hydrophobic sites of cellulose chains (hydrophobic 110 face) (Figure 3). This exposes the beta-D-glucopyranose rings in the chair conformation, which have their alpha and beta faces having either two or three axial hydrogens exposed and ring hydroxyl groups in the equatorial position, allowing the CBMs to bind efficiently (Nimlos, et al., 2007). The thermodynamic forces that drive this interaction is controversial, but most researchers postulate that it comes from the positive entropy when the water molecules are released from the protein and ligand (Boraston, et al., 2004). | ||
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== '''Mechanism''' == | == '''Mechanism''' == | ||
The CBM "pulls up" the chain and feeds it into the catalytic domain. As | [[Image:Mechanism.jpg]] | ||
The CBM "pulls up" the chain and feeds it into the catalytic domain. As mentioned before, the CBM's hydrophoic binding site of three tyrosines remains in contact with the surface throughout the reaction but can freely move translationally. The CBM undergoes a structural conformation after the substrate is in place. The fourth tyrosine (Y13) unfolds from within the CBM and forms a van der Waals interaction with the cellulose surface on the other side of the chain, thus encompassing the reducing end. While the rest of the CBM structure remains fairly rigid because of hydrogen bonds (between strand beta-3 and beta-1 and beta-2) and disulfide bridges (between beta-1 and beta-2) that maintain spacing matching that of the cellulose monomers at the binding site, the fourth tyrosine is located on the remainder of a loop of the protein and is more flexible for the induced fit (Nimlos, et al., 2007). Within the active site, Glutamine (212) acts as a catalytic nucleophile while Trypothan (40) fixes the substrate by hydrophoic interaction at the entrance of the active site tunnel. Similar to myosin and other motor proteins, the enzyme complex is driven by the hydrolysis of the glycosidic bond of cellulose (like phosphate bonds in ATP) as a source of energy for movement along their substrate (Igarashi, et al. 2009). | |||
== '''Applications''' == | == '''Applications''' == | ||
