Crystal structures of mammalian glutamine synthetases illustrate substrate-induced conformational changes and provide opportunities for drug and herbicide design.
Level 5 - mechanism / opinion, no new human data
In vitro structural biology and X-ray crystallography study with no human clinical data
PubMed 18005987 · doi:10.1016/j.jmb.2007.10.029
What was done
The authors solved and refined the first crystal structures of mammalian glutamine synthetase (GS): the apo form of canine GS at 3.0 Å resolution, human GS in complex with phosphate, ADP, and manganese at 2.05 Å resolution, and human GS complexed with phosphorylated methionine sulfoximine inhibitor, ADP, and manganese at 2.6 Å resolution. Structural conformations were compared across bacterial, plant, and mammalian enzymes.
What was found
Substrate binding, especially nucleotide binding, caused loop movements near the active site leading to a more closed conformation in eukaryotic GS. The amino acid substrate-binding pocket is highly conserved between bacterial and eukaryotic GS enzymes, whereas the nucleotide-binding site shows substantial structural divergence. Differences between mammalian and plant GS active sites were subtle.
Why it matters
By establishing that the nucleotide-binding site possesses greater species divergence than the amino acid-binding pocket, these structures guide the design of selective bacterial GS inhibitors and warn of cross-reactivity risks for herbicides targeting plant GS.
Limits
This is a bench-level structural study providing static crystallographic models; the abstract reports no binding kinetics, cellular assays, or functional validation of novel selective inhibitors.
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