Functional roles of the conserved Glu304 loop of Bacillus subtilis glutamine synthetase.
Functional roles of the conserved Glu304 loop of Bacillus subtilis glutamine synthetase.
复制标题
枯草芽孢杆菌谷氨酰胺合成酶保守 Glu304 环的功能作用。
DOI：
10.1128/jb.00509-10
复制
发表时间：
2010
影响因子：
3.2
通讯作者：
Fisher,SusanH
中科院分区：
文献类型：
--
作者：
WrayJr,LewisV;Fisher,SusanH
The enzymatic activity ofBacillus subtilisglutamine synthetase (GS), which catalyzes the synthesis of glutamine from ammonium and glutamate, is regulated by glutamine feedback inhibition. The feedback-inhibited form ofB. subtilisGS regulates the DNA-binding activities of the TnrA and GlnR nitrogen transcriptional factors. Bacterial GS proteins contain a flexible seven-residue loop, the Glu304 flap, that closes over the glutamate entrance to the active site. Amino acid substitutions in Glu304 flap residues were examined for their effects on gene regulation, enzymatic activity, and feedback inhibition. Substitutions in five of the Glu304 loop residues resulted in constitutive expression of both TnrA- and GlnR-regulated genes, indicating that this flap is important for regulating the activity of these transcription factors. The residues in the highly conserved Glu304 flap appear to be optimized for glutamate binding because mutant enzymes with substitutions in five of the flap residues had increased glutamateKmvalues compared to that for wild-type GS. The E304A and E304D substitutions increased the ammoniumKmvalues compared to that for wild-type GS and conferred high-level resistance to inhibition by glutamine, glycine, and methionine sulfoximine. A model for the role of the Glu304 residue in glutamine feedback inhibition is proposed.
