期刊
JOURNAL OF MOLECULAR BIOLOGY
卷 392, 期 2, 页码 334-351出版社
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2009.06.080
关键词
calmodulin-mediated activation; plant development and stress response; glutamate decarboxylase; pyridoxal 5 '-phosphate; protein-protein interactions
资金
- Swiss NCCR Structural Biology
- University of Verona
- EU design study SAXIER [RIDS 011934]
Glutamate decarboxylase (Gad) catalyzes glutamate to gamma-aminobutyrate conversion. Plant Gad is a similar to 340 kDa hexamer, involved in development and stress response, and regulated by pH and binding of Ca2+/calmodulin (CaM) to the C-terminal domain. We determined the crystal structure of Arabidopsis thaliana Gad1 in its CaM-free state, obtained a low-resolution structure of the calmodulin-activated Gad complex by small-angle X-ray scattering and identified the crucial residues, in the C-terminal domain, for regulation by pH and CaM binding. CaM activates Gad1 in a unique way by relieving two C-terminal autoinhibition domains of adjacent active sites, forming a 393 kDa Gad1-CaM complex with an unusual 1:3 stoichiometry. The complex is loosely packed: thanks to the flexible linkers connecting the enzyme core with the six C-terminal regulatory domains, the CaM molecules retain considerable positional and orientational freedom with respect to Gad1. The complex thus represents a prototype for a novel CaM-target interaction mode. Thanks to its two levels of regulation, both targeting the C-terminal domain, Gad can respond flexibly to different kinds of cellular stress occurring at different pH values. (C) 2009 Elsevier Ltd. All rights reserved.
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