Browsing by Author "Belrhali, Hassan"

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    Crystal structure of Type III glutamine synthetase: surprising reversal of the inter-ring interface
    (Elsevier, 2011) van Rooyen, Jason M; Abratt, Valerie R; Belrhali, Hassan; Sewell, Trevor
    Glutamine synthetases are ubiquitous, homo-oligomeric enzymes essential for nitrogen metabolism. Unlike types I and II, which are well described both structurally and functionally, the larger, type IIIs are poorly characterized despite their widespread occurrence. An understanding of the structural basis for this divergence and the implications for design of type-specific inhibitors has, therefore, been impossible. The first crystal structure of a GSIII enzyme, presented here, reveals a conservation of the GS catalytic fold but subtle differences in protein-ligand interactions suggest possible avenues for the design GSIII inhibitors. Despite these similarities, the divergence of the GSIII enzymes can be explained by differences in quaternary structure. Unexpectedly, the two hexameric rings of the GSIII dodecamer associate on the opposite surface relative to types I and II. The diversity of GS quaternary structures revealed here suggests a nonallosteric role for the evolution of the double-ringed architecture seen in all GS enzymes.
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    Proteolysis of the type III glutamine synthetase from Bacteroides fragilis causes expedient crystal-packing rearrangements
    (International Union of Crystallography, 2011) Rooyen, Jason van; Belrhali, Hassan; Abratt, Valarie; Sewel, Trevor B
    This work details the intentional modifications that led to the first structure of a type III glutamine synthetase enzyme (GSIII). This approach followed the serendipitous discovery of digestion caused by an extracellular protease from a contaminating bacterium, Pseudomonas fluorescens. The protease only cleaves the GSIII protein at a single site, leaving the oligomer intact but allowing the protein to crystallize in a different space group. This transition from space group P1 to space group C2221 is accompanied by improved growth characteristics, more reproducible diffraction and enhanced mechanical stability. The crystallographic analyses presented here provide the structural basis of the altered molecular packing in the full-length and digested crystal forms and suggest modifications for future structural studies.
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    Proteolysis of the type III glutamine synthetase from Bacteroides fragilis causes expedient crystal-packing rearrangements
    (International Union of Crystallography, 2011) van Rooyen, Jason; Belrhali, Hassan; Abratt, Valarie; Sewella, Trevor B
    This work details the intentional modifications that led to the first structure of a type III glutamine synthetase enzyme (GSIII). This approach followed the serendipitous discovery of digestion caused by an extracellular protease from a contaminating bacterium, Pseudomonas fluorescens. The protease only cleaves the GSIII protein at a single site, leaving the oligomer intact but allowing the protein to crystallize in a different space group. This transition from space group P1 to space group C2221 is accompanied by improved growth characteristics, more reproducible diffraction and enhanced mechanical stability. The crystallographic analyses presented here provide the structural basis of the altered molecular packing in the full-length and digested crystal forms and suggest modifications for future structural studies.