Protein of the Week: glutamine synthetase
Glutamine synthetase (PDB code 2GLS, structure generated with PyMOL) provides a mechanism for cells to dispose of excess nitrogen when they break down proteins (and amino acids) for energy. It converts glutamate to glutamine at the cost of an ATP. The glutamine then travels to the liver and drops off the ammonium at the end of its R group.
Active glutamine synthetase is composed of two hexamer layers that communicate with each other the amount of products downstream of glutamine. The symmetry is beautiful in its own right.
When the protein is turned on its side, the interaction between the hexamers is readily apparent.