Abstract

Glutamine synthetase (GS) catalyzes the ligation of glutamate and ammonia to form glutamine, with concomitant hydrolysis of ATR In mammals, the activity eliminates cytotoxic ammonia, at the same time converting neurotoxic glutamate to harmless glutamine; there are a number of links between changes in GS activity and neurodegenerative disorders, such as Alzheimer's disease. In plants, because of its importance in the assimilation and re-assimilation of ammonia, the enzyme is a target of some herbicides. GS is also a central component of bacterial nitrogen metabolism and a potential drug target. Previous studies had investigated the structures of bacterial and plant GSs. In the present publication, we report the first structures of mammalian GSs. The apo form of the canine enzyme was solved by molecular replacement and refined at a resolution of 3 A. Two structures of human glutamine synthetase represent complexes with: a) phosphate, ADP, and manganese, and b) a phosphorylated form of the inhibitor methionine sulfoximine, ADP and manganese; these structures were refined to resolutions of 2.05 angstrom and 2.6 angstrom, respectively. Loop movements near the active site generate more closed forms of the eukaryotic enzymes when substrates are bound; the largest changes are associated with the binding of the nucleotide. Comparisons with earlier structures provide a basis for the design of drugs that are specifically directed at either human or bacterial enzymes. The site of binding the amino acid substrate is highly conserved in bacterial and eukaryotic GSs, whereas the nucleotide binding site varies to a much larger degree. Thus, the latter site offers the best target for specific drug design. Differences between mammalian and plant enzymes are much more subtle, suggesting that herbicides targeting GS must be designed with caution. (c) 2007 Elsevier Ltd. All rights reserved.

Keywords

glutamine synthetase; X-ray crystallography; conformational changes; drug design; herbicide

Published in

Journal of Molecular Biology
2008, Volume: 375, number: 1, pages: 217-228

SLU Authors

• Mowbray, Sherry

  • Department of Molecular Biology, Swedish University of Agricultural Sciences
    

Sustainable Development Goals

Ensure healthy lives and promote well-being for all at all ages


UKÄ Subject classification

Food Science


Publication identifier

DOI: https://doi.org/10.1016/j.jmb.2007.10.029

Permanent link to this page (URI)

https://res.slu.se/id/publ/30884