AI Article Synopsis
- GUN4 is a conserved regulator of chlorophyll biosynthesis found in almost all oxygen-producing photosynthetic organisms, playing a key role in binding bilins and stimulating magnesium chelatase activity in algae.
- Recent studies characterized GUN4 from Arabidopsis thaliana and Synechocystis sp. PCC 6803, revealing crystal structures of GUN4 bound to different bilins at high resolutions.
- The research suggests that bilins adopt a cyclic-helical conformation, strengthening their binding to GUN4 and implies GUN4's involvement in regulating the tetrapyrrole biosynthesis pathway and its role in retrograde signaling.
Article Abstract
The 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 Å, 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.
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| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8442963 | PMC |
| http://dx.doi.org/10.1002/pro.4164 | DOI Listing |
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