Electron microscopy of multiple forms of glutamine synthetase from bacteroids and the cytosol of yellow lupin root nodules

The three-dimensional structure of an eukaryotic glutamine synthetase: Functional implications of its oligomeric structure

“…Although several electron microscopy studies have been performed with GS-II enzymes (Pushkin et al, 1981(Pushkin et al, , 1985Tsuprun et al, 1987;Boksha et al, 2002), which in some cases have resulted in a model of the oligomeric state of the enzyme, no three-dimensional reconstruction of any GS-II has to our knowledge been so far reported. Recently, a three-dimensional structure of human GS-II was generated that depicts GS-II as a double heptamer (Kiang, 2001).…”

“…Nevertheless, the oligomeric state of GS-II has been the subject of study for more than two decades and several models have been generated, based on electron microscopy and biochemical studies, which point to GS-II as an octamer made by two superimposed rings formed in turn by four identically placed subunits (McParland et al, 1976;Pushkin et al, 1981Pushkin et al, , 1985Tsuprun et al, 1987;Boksha et al, 2002). Some of these studies suggest a shift between the two tetrameric rings of 40° (Pushkin et al, 1981(Pushkin et al, , 1985Tsuprun et al, 1987). More recent electron microscopy results point to GS-II as a double heptamer (Kiang, 2001).…”

Rhizobium meliloti 1021 has three differentially regulated loci involved in glutamine biosynthesis, none of which is essential for symbiotic nitrogen fixation

“…In contrast to enteric bacteria, members of the family Rhizobiaceae, including Rhizobium, Bradyrhizobium, and Agrobacterium species, contain at least two distinct forms of GS (13,27,38,62). GSI is a homolog of the ginA gene product of enteric bacteria in terms of its heat stability, molecular mass (monomer -55,000 daltons), subunit struc-ture (12 subunits), and adenylylation properties.…”