Sandbox108
From Proteopedia
Glutamine synthetase assignment by UMBC undergraduate students
Glutamine synthetase of Salmonella typhimurium
Tertiary structure of protein is characterized by the “global” folding of a polypeptide chain [1] and mostly affected by Hydrophobic(purple)(polar(blue)) interaction and hydrogen bonding. In general, hydrophobic interaction is a major driving force determining the most tertiary structure of the proteins. Hydrogen bonding is crucial in stabilizing the tertiary structure as well.[2] Also, disulfide bonds stabilize the tertiary structure in residues such as cysteine residues.[3] However, for Salmonella typhimurium it is mostly influenced by the helix-helix interactions between 12-subunits enzymes within two layers.[4]
Glutamine synthetase from Salmonella typhimurium is the 12-subunits enzyme, and has 23 helix-helix interactions involving helices of chain A with four different types of interactions. [5] The 12-subunits enzyme are arranged in two layers of six, such as Glu-131 which is the one of the protein residues of Salmonella typhimurium; at the interface of pairs of subunits within each layer, six anti-parallel beta strands formed cylindrical active sites.[6] Each active site holds two Mn2+ ions surrounded by some histidyl side chains. [7] Also, the protein ligands to Mn2+ 469 are Glu-131, Glu-212, and Glu-220; those to Mn2+ 470 are Glu-129, His-269, and Glu-357.[8] Glutamine from Salmonella typhimurium has 12-subunits of each of them in pairs within two layers. C-terminus end of the polypetide and a helical thong, which inserts into a Hydrophobic(purple) pocket formed by two neighboring subunits on the opposite ring, hold the two layers of subunits tightly.[9] Also, hydrogen-bonded beta sheet interactions(black) can affect the form of tertiary structure, but Hydrophobic(purple) interactions will contribute to the stability of the intersubunit between two layers more efficiently.[10] In the other hand, the most effective interaction in glutamine synthetase from Salmonella typhimurium is the helix-helix interactions. The folding of the proteins can be affected by the 12-subunits in the residues. In the case of Salmonella typhimurium the helices of chain A has the charged regions(blue and red), while most glutamine has uncharged side chain which formed by replacing the hydroxyl of glutamic acid with an amine functional group. Moreover, glutamine from Salmonella typhimurium has two domains; "beta-grasp domain" and "catalytic domain."[11][12] In short, this is N-terminal and C-terminal domain.[13] The N-terminal domain refers to the end of a polypeptide which has a free amine group,[14] and the C-terminal end of the polypeptide has a free carboxyl group.[15] As a result, glutamine synthetase for Salmonella typhimurium depends mostly on the helix-helix interactions involving helices with four different types of interactions. 12-subunits enzymes are arranged in two layers of six, where the hydrogen-bonded beta sheet and hydrophobic interactions occur.
