Sandbox Reserved 770: Difference between revisions
From Proteopedia
Jump to navigationJump to search
Bryan Toton (talk | contribs) |
Bryan Toton (talk | contribs) |
||
| Line 60: | Line 60: | ||
The central core within each monomer of PAL contains three central alpha helices of triple-coiled coils (Helix 3,Helix 4, and Helix 7), improving its rigidity similar to fibrous proteins in keratin. The three core helices are oriented with similarly aligned dipoles to create an electro-positive platform for cofactor 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO, Figure 5.) to anchor through noncovalent bonding, shown in Figure 4b. Covalent linkages between cofactor MIO and PAL backbone act to direct the C-terminus of MIO to an alpha helix's N-terminus, creating a loop, thus the helix's positive pole points toward the cofactor and the active site. | The central core within each monomer of PAL contains three central alpha helices of triple-coiled coils (Helix 3,Helix 4, and Helix 7), improving its rigidity similar to fibrous proteins in keratin. The three core helices are oriented with similarly aligned dipoles to create an electro-positive platform for cofactor 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO, Figure 5.) to anchor through noncovalent bonding, shown in Figure 4b. Covalent linkages between cofactor MIO and PAL backbone act to direct the C-terminus of MIO to an alpha helix's N-terminus, creating a loop, thus the helix's positive pole points toward the cofactor and the active site. | ||
[[Image:Positive_Negative_Helices_PAL.png|thumb|left|Figure 6. Six positive poles toward the active site, one negative pole toward the active site]] | |||
==Active Sites== | ==Active Sites== | ||
| Line 65: | Line 68: | ||
PAL active site contains a highly conserved Ala-Ser-Gly triad. Post-translational modification of an electrophilic prostetic group MIO formed autocatalytically by cyclization and dehydration of PAL's active site. MIO provides the surface for phenylalanine conversion to produce trans-cinnamic acid and ammonia. | PAL active site contains a highly conserved Ala-Ser-Gly triad. Post-translational modification of an electrophilic prostetic group MIO formed autocatalytically by cyclization and dehydration of PAL's active site. MIO provides the surface for phenylalanine conversion to produce trans-cinnamic acid and ammonia. | ||
Most of the conserved active site residues are contained within seven stabilizing alpha helices. These residues include: Leu266, Asn270, Val269, Leu215, Lys486, and Ile472.<ref name=rutgers>http://maptest.rutgers.edu/drupal/?q=node/408</ref> Six positive alpha helices point toward the active site in association with MIO cofactor. This association will not only increase the electrophilicity of MIO, but also increases he positive charge of highly conserved Lys468 residue. The positive poles are suitable for stabilizing a carbanionic charge produced by an elimination unimolecular conjugate base (E1cB) mechanism of substrate phenylalanine, in accordance with MIO cofactor. Stabilization of the carbanion reduces pKa of the C3 methylidine group of phenylalanine, promoting the interactions between the negatively charged carboxylate end of phenylalanine to the active site of PAL. | Most of the conserved active site residues are contained within seven stabilizing alpha helices, represented by Figure 6. These residues include: Leu266, Asn270, Val269, Leu215, Lys486, and Ile472.<ref name=rutgers>http://maptest.rutgers.edu/drupal/?q=node/408</ref> Six positive alpha helices point toward the active site in association with MIO cofactor. This association will not only increase the electrophilicity of MIO, but also increases he positive charge of highly conserved Lys468 residue. The positive poles are suitable for stabilizing a carbanionic charge produced by an elimination unimolecular conjugate base (E1cB) mechanism of substrate phenylalanine, in accordance with MIO cofactor. Stabilization of the carbanion reduces pKa of the C3 methylidine group of phenylalanine, promoting the interactions between the negatively charged carboxylate end of phenylalanine to the active site of PAL. | ||
==Conserved Residues in Catalysis== | ==Conserved Residues in Catalysis== | ||
