 |
PDBsum entry 1pv8
|
|
|
|
|
 |
Contents |
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
* Residue conservation analysis
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Control of tetrapyrrole biosynthesis by alternate quaternary forms of porphobilinogen synthase.
|
|
|
Authors
|
|
S.Breinig,
J.Kervinen,
L.Stith,
A.S.Wasson,
R.Fairman,
A.Wlodawer,
A.Zdanov,
E.K.Jaffe.
|
|
|
Ref.
|
|
Nat Struct Biol, 2003,
10,
757-763.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
Figure 1.
Figure 1. Characteristics of wild-type human PBGS relative to
the F12L variant. (a) The pH-rate profile for human PBGS (
 )
exhibits a two-proton activating pK[a] of 5.9 and a one-proton
deactivating pK[b] of 8.3. In contrast, the F12L variant (  )
shows a single one-proton activating pK[a] of 8.5. (b) The
chromatographic separation of wild-type human (WT) PBGS and the
F12L variant on a mono-Q column. (c) The differential mobility
of wild-type (WT) human PBGS and the F12L variant on 12.5% (w/v)
native PAGE.
|
|
Figure 3.
Figure 3. Characteristics of coexpressed WT+F12L. (a)
Separation of two peaks of PBGS protein on Q-Sepharose; KCl
gradient (red line), A (black
line). Both pools showed PBGS activity at pH 7 (  )
and at pH 9 ( ).
(b) The mobility of the two pools of WT+F12L relative to
wild-type (WT) human PBGS and the F12L variant on native gel
electrophoresis. (c) The pH-rate profiles for pool I ( )
and pool II ( )
after further purification on Sephacryl S300. (d) Determination
of K[m] and V[max] values for the S300 purified pool I ( )
and pool II ( [280][glyph.gif] ) at pH 7 (black) and pH 9 (red).
Dashed lines indicate the poor fits to standard hyperbolic
saturation kinetics. Solid lines indicate the superior fit to a
double hyperbola model where two forms of the enzyme are
catalyzing the same reaction (see text and Table 1).
|
|
|
|
|
|
The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nat Struct Biol
(2003,
10,
757-763)
copyright 2003.
|
|
|
|
|
|
|
