title: Control of tetrapyrrole biosynthesis by alternate quaternary forms of porphobilinogen synthase.
abstract: Porphobilinogen synthase (PBGS) catalyzes the first common step in the biosynthesis of tetrapyrroles (such as heme and chlorophyll). Although the predominant oligomeric form of this enzyme, as inferred from many crystal structures, is that of a homo-octamer, a rare human PBGS allele, F12L, reveals the presence of a hexameric form. Rearrangement of an N-terminal arm is responsible for this oligomeric switch, which results in profound changes in kinetic behavior. The structural transition between octamer and hexamer must proceed through an unparalleled equilibrium containing two different dimer structures. The allosteric magnesium, present in most PBGS, has a binding site in the octamer but not in the hexamer. The unprecedented structural rearrangement reported here relates to the allosteric regulation of PBGS and suggests that alternative PBGS oligomers may function in a magnesium-dependent regulation of tetrapyrrole biosynthesis in plants and some bacteria.
authors.affiliation: Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, Pennsylvania 19111-2497, USA.
authors.forename: Sabine
authors.initials: S
authors.lastname: Breinig
authors.forename: Jukka
authors.initials: J
authors.lastname: Kervinen
authors.forename: Linda
authors.initials: L
authors.lastname: Stith
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Wasson
authors.forename: Robert
authors.initials: R
authors.lastname: Fairman
authors.forename: Alexander
authors.initials: A
authors.lastname: Wlodawer
authors.forename: Alexander
authors.initials: A
authors.lastname: Zdanov
authors.forename: Eileen K
authors.initials: EK
authors.lastname: Jaffe
mesh_terms: D000495:Allosteric Site; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002734:Chlorophyll / Q000737:chemistry; D006224:Cricetinae; D018360:Crystallography, X-Ray; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000494:pharmacology; D005982:Glutathione Transferase / Q000378:metabolism; D006418:Heme / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D008958:Models, Molecular; D010944:Plants / Q000378:metabolism; D000623:Porphobilinogen Synthase / Q000737:chemistry*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011758:Pyrroles; D045725:Tetrapyrroles; D014461:Ultracentrifugation
chemical_list: D011758:Pyrroles; D045725:Tetrapyrroles; D002734:Chlorophyll; D006418:Heme; D004492:Edetic Acid; D005982:Glutathione Transferase; D000623:Porphobilinogen Synthase; D008274:Magnesium