Speaker
Mrs
shabnam Tarahi Tabrizi
(macquarie university)
Description
The magnesium chelatase enzyme catalyses the ATP dependent insertion of Mg+ in to protoporphyrin IX(PPIX) in the first step of the chlorophyll biosynthesis pathway consists three different protein subunits ChlI ChlD and ChlH. The GUN4 protein is a regulatory subunit of Mg-chelatase that binds the chlorophyll biosynthesis intermediates, PPIX and Mg protoporphyrin(Mg-PPIX), stimulates Mg chelatase activity, and is implicated in developmental signaling pathway between the chloroplast and nucleus. ChlH is the largest subunit of Mg-chelatase which also binds both PPIX substrate and the Mg-PPIX product. GUN4 appears to participate in a plastid-to-nucleus signalling pathway possibly through regulating Mg-PPIX synthesis or trafficking. Unlike the cyanobacterial GUN4, the chloroplastic orthologous have an extra C-terminal domain that is phosphorylated and is required for magnesium chelatase activity. We have determined the low resolution solution structure of GUN4 , H and the GUN4-H-PPIX complex at ~20 A°, by using (SAXS) small-angle x-ray scattering and can report that the GUN4 protein has a more elongated structure compared to the cyanobacterial protein. Furthermore, The SAXS structure of the GUN4-H-PPIX complex is similar to the SAXS structure of H subunit suggesting that GUN4–PPIX may attach somewhere inside the cage shape structure of H subunit to form a complex.
| Keywords or phrases (comma separated) | Mg-chelatase, GUN4, ChlH |
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Primary author
Mrs
shabnam Tarahi Tabrizi
(macquarie university)
Co-authors
Dr
Anthony Duff
(ANSTO)
Prof.
Robert Willows
(Macquarie University)
