User:Tom Gluick/glutamine synthetase/Assignment 1

StoichiometryStoichiometry

Quarternary Structure

The enzyme Glutamine Synthetase is made up of twelve subunits. The structure consists of two identical hexameric rings held together by hydrophobic and hydrogen bonding forces. The N-terminal helix of each subunit is exposed to hydrophilic solvent, where as the C-terminal is enshrouded in hydrophobic regions within the helical structure of the rings. The central channel is linked together by six four-stranded anti-parallel L-sheets which along with the twelve monomers enhance the stability of the protein structure.

Quarternary Interactions

The subunits are connected through couple of different type of interactions, such as: Hydrogen Bonds, and Non-bonded contacts. Each subunit has area’s that are proportional to the surface area of the corresponding protein chains. Each subunit only interacts with four other protomers in the protein.

Subunit Connections:

A interacts with four subunits, F, G, H, and B.

B interacts with four subunits, H, I, A, and C.

C interacts with four subunits, B, D, I, and J.

D interacts with four subunits, C, I, J, and K.

E interacts with four subunits, L, F, D, and K.

F interacts with four subunits, A, G, L, and E.

G interacts with four subunits, A, H, L, and F.

H interacts with four subunits, A, B, G, and L.

I interacts with four subunits, B, H, C, and J.

J interacts with four subunits, I, C, D, and K.

K interacts with four subunits, E, L, J, and D.

L interacts with four subunits, E, F, A, and G.

Active SiteActive Site

Glutamine Synthetase is dodecameric and has 622 symmetry. Each active site is located at an interface between subunits, and is made up of residues from two adjacent subunits. The is between two protomers and indicated by the yellow manganese atoms highlighted in the applet. The can be described as a 'bifunnel' in which ATP and glutamate bind at opposite ends. It is surrounded by three important ligands: ADP, TL as labeled in the applet. ADP is short for Adenosite Diphosphate. And the metal ion, Thallium is also labeled in the applet.

ReferenceReference

1. Eisenberg, David and Gill, Harindarpal and Pfluegl, Gaston and Rotstein, Sergio. “Structure-function relationships of glutamine synthetases.” Elsevier, archives of biochemistry and biophysics 1477(Dec 1999):122-123.

2. Eisenberg, Gill. "Crystal structure of glutamine synthetase from salmonella typhimurium with thallium ions" PDBsum. european bioinformatics institute 2006-2008. <http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=1f1h&template=main.html>