title: Structure of GUN4 from Chlamydomonas reinhardtii.
abstract: The genomes uncoupled 4 (GUN4) protein stimulates chlorophyll biosynthesis by increasing the activity of Mg-chelatase, the enzyme that inserts magnesium into protoporphyrin IX (PPIX) in the chlorophyll biosynthesis pathway. One of the roles of GUN4 is in binding PPIX and Mg-PPIX. In eukaryotes, GUN4 also participates in plastid-to-nucleus signalling, although the mechanism for this is unclear. Here, the first crystal structure of a eukaryotic GUN4, from Chlamydomonas reinhardtii, is presented. The structure is in broad agreement with those of previously solved cyanobacterial structures. Most interestingly, conformational divergence is restricted to several loops which cover the porphyrin-binding cleft. The conformational dynamics suggested by this ensemble of structures lend support to the understanding of how GUN4 binds PPIX or Mg-PPIX.
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW 2109, Australia.
authors.forename: Shabnam
authors.initials: S
authors.lastname: Tarahi Tabrizi
authors.affiliation: Garvan Institute of Medical Research, Darlinghurst, Sydney, NSW 2010, Australia.
authors.forename: David B
authors.initials: DB
authors.lastname: Langley
authors.affiliation: Australian Synchrotron, 800 Blackburn, Clayton, Melbourne, VIC 3168, Australia.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Harrop
authors.affiliation: ANSTO, Lucas Heights, NSW 2234, Australia.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Duff
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW 2109, Australia.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Willows
mesh_terms: D020418:Algal Proteins / Q000737:chemistry* / Q000235:genetics; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D016825:Chlamydomonas reinhardtii / Q000737:chemistry* / Q000235:genetics; D003001:Cloning, Molecular; D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011524:Protoporphyrins / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D020418:Algal Proteins; D011524:Protoporphyrins; D011993:Recombinant Fusion Proteins; C039629:magnesium protoporphyrin; C028025:protoporphyrin IX
keywords: chlorophyll biosynthesis; genomes uncoupled; magnesium chelatase; plastid signalling; protoporphyrin