Structure
Glutamine Synthetase can be composed of 8, 10, or 12 identical subunits separated into two face-to-face rings. Bacterial GS are dodecamers with 12 active sites between each monomer. Each active site creates a ‘bifunnel’ which is the site of three distinct substrate binding sites: nucleotide, ammonium ion, and amino acid. ATP binds to the top of the bifunnel that opens to the external surface of GS. Glutamate binds at the bottom of the active site. The middle of the bifunnel contains two sites in which divalent cations bind (Mn+2 or Mg+2). One cation binding site is involved in phosphoryl transfer of ATP to glutamate, while the second stabilizes active GS and helps with the binding of glutamate.
Hydrogen bonding and hydrophobic interactions hold the two rings of GS together. Each subunit possesses a C-terminus and an N-terminus in its sequence. The C-terminus (helical thong) stabilizes the GS structure by inserting into the hydrophobic region of the subunit across in the other ring. The N-terminus is exposed to the solvent. In addition, the central channel is formed via six four-stranded β-sheets composed of anti-parallel loops from the twelve subunits.
Read more about this topic: Glutamine Synthetase
Famous quotes containing the word structure:
“If rightly made, a boat would be a sort of amphibious animal, a creature of two elements, related by one half its structure to some swift and shapely fish, and by the other to some strong-winged and graceful bird.”
—Henry David Thoreau (1817–1862)
“When a house is tottering to its fall,
The strain lies heaviest on the weakest part,
One tiny crack throughout the structure spreads,
And its own weight soon brings it toppling down.”
—Ovid (Publius Ovidius Naso)
“With sixty staring me in the face, I have developed inflammation of the sentence structure and definite hardening of the paragraphs.”
—James Thurber (1894–1961)