20-21 November 2014
National Centre for Synchrotron Science
Australia/Melbourne timezone
Save the date: User Meeting 2015 - 26-27 November

Structure characterization of the Chlamydomonas reinhardtii magnesium chelatase GUN4 and H subunits by small-angle X-ray scattering

20 Nov 2014, 17:30
1h 30m
NCSS Exhibition Area ()

NCSS Exhibition Area

Australian Synchrotron 800 Blackburn Road Clayton VIC 3168
Board: 1009


Mrs shabnam Tarahi Tabrizi (macquarie university)


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

Primary author

Mrs shabnam Tarahi Tabrizi (macquarie university)


Dr Anthony Duff (ANSTO) Prof. Robert Willows (Macquarie University)

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