Glutamine synthetases of pea leaf and seed cytosol. Structure and properties

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).…”

Structure–function relationships of glutamine synthetases

“…Early monomer molecular weights, on the other hand, before the sequence was known, seem to be estimated by dividing the measured complex weight by eight. The monomer molecular weight determined from sequence (M r V42 kDa) is much smaller [91,100,101], than the values given in earlier papers [72,83,99]. Based on sedimentation experiments (velocity and equilibrium) and knowledge of the monomer molecular weight, the calculated number of subunits for the GS II complex varies from the generally agreed eight: GS II consists of 11 subunits in pea seed cytosol [99], nine subunits in pig brain [72], 10^13 subunits in sheep brain [81,83] and 11 subunits in human GS (P£uegl, G.M.U, unpublished results).…”

“…The monomer molecular weight determined from sequence (M r V42 kDa) is much smaller [91,100,101], than the values given in earlier papers [72,83,99]. Based on sedimentation experiments (velocity and equilibrium) and knowledge of the monomer molecular weight, the calculated number of subunits for the GS II complex varies from the generally agreed eight: GS II consists of 11 subunits in pea seed cytosol [99], nine subunits in pig brain [72], 10^13 subunits in sheep brain [81,83] and 11 subunits in human GS (P£uegl, G.M.U, unpublished results). The di¡erence in number of subunits determined by sedimentation or by electron micrographs is to date not explainable, although it has been pointed out that interpretations of analytical ultracentrifugation, gel ¢ltration and negative staining electron microsco-py studies of oligomeric protein subunit stoichiometry are often ambiguous [102].…”

“…Another discrepancy in studies of GS II is its molecular weight, which ranges in reports from 352 kDa for rat liver GS [70], 370 kDa for pig brain GS [72], 430, 497 and 525 kDa for sheep brain GS [81,83], to 520 kDa for pea leaf cytosol GS [99]. Based on electron micrographs, it has been postulated that GS II is an octamer that consists of two stacked tetramers with D4 symmetry [72].…”