Sandbox Reserved 770: Difference between revisions

[[Image:Tertiary Structure.gif|thumb|left|Figure 4. Tertiary structure of PAL. The three central core helices, leading to the active site, are colored blue, green, and yellow. (a) Stereoview of the PAL monomer with residue numbering. (b) Stereoview of MIO and Phe413 interactions with the three central helices, polarized with their N termini directed toward the active site. Hydrogen bonds are indicated by dashed lines. <ref name=crystal>http://pubs.acs.org.prox.lib.ncsu.edu/doi/pdfplus/10.1021/bi049053%2B</ref>]]

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) 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.