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==Glutamine synthetase assignment by UMBC undergraduate students==
{{STRUCTURE_2gls |  PDB=2gls  |  SCENE=  }}

== OUTLINE ==

''Glutamine synthetase of Salmonella typhimurium''


Tertiary structure of protein is characterized by the “global” folding of a polypeptide chain [http://www.stanford.edu/group/pandegroup/folding/education/prstruc.html] and has two domains in refined atomic model of glutamine synthetase from Salmonella typhimurium. Hydrophobic interaction is a major driving force determining the most tertiary structure of the proteins. [http://www.stanford.edu/group/pandegroup/folding/education/prstruc.html] Hydrogen bonding is crucial in stabilizing the tertiary structure as well. [http://webhost.bridgew.edu/fgorga/proteins/proteins.htm] Also, disulfide bonds between cysteine residues stabilize the tertiary structure. [http://webhost.bridgew.edu/fgorga/proteins/proteins.htm] However, for glutamine synthetase for Salmonella, the most important interaction will be the helix-helix interactions. 


Glutamine synthetase from Salmonella typhimurium is the 12-subunit enzyme and has 23 helix-helix interactions involving helices of chain A with four different types of interactions. [http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=2gls&template=protein.html&o=HELIX_INTERACTIONS&l=1&s=1&c=7&chain=A]          

{the 12 subunits are arranged in two layers of six; at the interface of pairs of subunits within each layer, cylindrical active sites are formed by six anti-parallel beta strands contributed by one subunit and two strands by the neighboring subunit. This interpretation of the electron density map has now been supported by comparison with glutamine synthetase from Escherichia coli by the Fourier difference method. Each active site cylinder holds two Mn2+ ions, with each ion having as ligands three protein side chains and two water molecules (one water shared by both metals), as well as a histidyl side chain just beyond liganding distance. The protein ligands to Mn2+ 469 are <scene name='Sandbox108/Glu_131/1'>Glu-131</scene>, Glu-212, and Glu-220; those to Mn2+ 470 are Glu-129, His-269, and Glu-357. The two layers of subunits are held together largely by the apolar COOH terminus, a helical thong, which inserts into a hydrophobic pocket formed by two neighboring subunits on the opposite ring. Also between layers, there is a hydrogen-bonded beta sheet interaction, as there is between subunits within a ring, but hydrophobic interactions account for most of the intersubunit stability. The central loop, which extends into the central aqueous channel, is subject to attack by at least five enzymes and is discussed as an enzyme "passive site."}[http://www.ncbi.nlm.nih.gov/pubmed/2572586?dopt=Abstract]

Helix-helix interactions are the only interaction that can affect the folding of the proteins in Salmonella typhimurium. <scene name='Sandbox108/Hydrophobic/1'>Hydrophobic(purple)</scene> and <scene name='Sandbox108/Polar/1'>polar(blue)</scene> regions of the protein residues are on the helices of chain A. Also, uncharged polar groups are usually classified as hydrophilic that is found on the outside of proteins, but for glutamine in Salmonella typhimurium its side chain is uncharged and formed by replacing the hydroxyl of glutamic acid with an amine functional group. [http://en.wikipedia.org/wiki/Glutamine] Moreover, on the helices of chain A has <scene name='Sandbox108/Charged_region/1'>the charged regions(blue and red)</scene>.