7e2r
The ligand-free structure of Arabidopsis thaliana GUN4
Structural highlights
FunctionGUN4C_ARATH Regulates chlorophyll synthesis and plastid-to-nucleus signal transduction by binding both the product and the substrate of Mg-chelatase, an enzyme that produces magnesium-protoporphyrin IX (Mg-Proto). Activates also Mg-chelatase. Neither binds abscisic acid (ABA) nor is involved in ABA signaling.[1] [2] Publication Abstract from PubMedThe chlorophyll biosynthesis regulator GENOMES UNCOUPLED 4 (GUN4) is conserved in nearly all oxygenic photosynthetic organisms. Recently, GUN4 has been found to be able to bind the linear tetrapyrroles (bilins) and stimulate the magnesium chelatase activity in the unicellular green alga Chlamydomonas reinhardtii. Here, we characterize GUN4 proteins from Arabidopsis thaliana and the cyanobacterium Synechocystis sp. PCC 6803 for their ability to bind bilins, and present the crystal structures of Synechocystis GUN4 in biliverdin-bound, phycocyanobilin-bound, and phytochromobilin-bound forms at the resolutions of 1.05, 1.10, and 1.70 A, respectively. These linear molecules adopt a cyclic-helical conformation, and bind more tightly than planar porphyrins to the tetrapyrrole-binding pocket of GUN4. Based on structural comparison, we propose a working model of GUN4 in regulation of tetrapyrrole biosynthetic pathway, and address the role of the bilin-bound GUN4 in retrograde signaling. Structural basis of bilin binding by the chlorophyll biosynthesis regulator GUN4.,Hu JH, Chang JW, Xu T, Wang J, Wang X, Lin R, Duanmu D, Liu L Protein Sci. 2021 Aug 11. doi: 10.1002/pro.4164. PMID:34382282[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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