210
V. Schünemann
Fig. 4.24 Mössbauer spectra of LytB (IspH) taken at 77 K with no applied field a and at 5 K in a
field of 5 T. The solid lines are spin Hamiltonian simulations assuming a diamagnetic [4Fe–4S] 2+
cluster. Reprinted with permission from [90]. Copyright (2009) American Chemical Society
malaria parasite Plasmodium falciparum. In these pathogens, isoprenoid synthesis
occurs according to the methylerythritol phosphate (MEP) pathway, an alternative
to the mevalonate pathway in higher organisms [89]. LytB catalyses the last step of
the MEP pathway. After initial crystal structure data indicate that this enzyme has an
3Fe–4S cluster Mössbauer spectroscopy clearly showed that LytB indeed harbours
a 4Fe–4S center as the active site [90]. Unlike other 4Fe–4S proteins the cluster of
LytB has a unique site which serves has a substrate binding site for (E)-4-hydroxy3-methylbut-2-en-1-yl diphosphate (HMBPP) in order to initiate HMBPP conversion into a mixture of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate
(DMAPP) [91].
The inspection of the Mössbauer spectrum of LytB shown in Fig. 4.24 indicates
the presence of a component with δ = 0.89 mms
−1 and ΔE Q = 1.97 mms
−1 . These
parameters are typical for high spin iron(II) and one could easily assume the presence of non-protein bound iron(II) in the sample under investigation. In this case a
Mössbauer spectrum taken at high field would induce spin expectation values and a
magnetically split pattern would be expected similar to the case of reduced rubredoxin (see Fig. 4.21). However, for LytB the Mössbauer spectrum taken at high fields
could be simulated with the spin Hamiltonian formalism under the assumption that
all components are diamagnetic. This can only be explained by the fact that the
ferrous high spin site is part of an unusual 4Fe–4S cluster with one Fe
2.5+ –Fe
2.5+ pair
having a spin of 9/2 and another more valence trapped “Fe
2+ –Fe
3+ ” pair having also
a spin of 9/2. An antiparallel spin arrangement than causes the diamagnetism of the
[4Fe–4S]
2+ cluster of LytB.
When the chemical substrate HMBP is added to the LytB protein the Mössbauer spectrum chances significantly (Fig. 4.25). An analysis of the data displayed
in Fig. 4.25b indicates that only the doublet representing the special iron(II) site is
V. Schünemann
Fig. 4.24 Mössbauer spectra of LytB (IspH) taken at 77 K with no applied field a and at 5 K in a
field of 5 T. The solid lines are spin Hamiltonian simulations assuming a diamagnetic [4Fe–4S] 2+
cluster. Reprinted with permission from [90]. Copyright (2009) American Chemical Society
malaria parasite Plasmodium falciparum. In these pathogens, isoprenoid synthesis
occurs according to the methylerythritol phosphate (MEP) pathway, an alternative
to the mevalonate pathway in higher organisms [89]. LytB catalyses the last step of
the MEP pathway. After initial crystal structure data indicate that this enzyme has an
3Fe–4S cluster Mössbauer spectroscopy clearly showed that LytB indeed harbours
a 4Fe–4S center as the active site [90]. Unlike other 4Fe–4S proteins the cluster of
LytB has a unique site which serves has a substrate binding site for (E)-4-hydroxy3-methylbut-2-en-1-yl diphosphate (HMBPP) in order to initiate HMBPP conversion into a mixture of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate
(DMAPP) [91].
The inspection of the Mössbauer spectrum of LytB shown in Fig. 4.24 indicates
the presence of a component with δ = 0.89 mms
−1 and ΔE Q = 1.97 mms
−1 . These
parameters are typical for high spin iron(II) and one could easily assume the presence of non-protein bound iron(II) in the sample under investigation. In this case a
Mössbauer spectrum taken at high field would induce spin expectation values and a
magnetically split pattern would be expected similar to the case of reduced rubredoxin (see Fig. 4.21). However, for LytB the Mössbauer spectrum taken at high fields
could be simulated with the spin Hamiltonian formalism under the assumption that
all components are diamagnetic. This can only be explained by the fact that the
ferrous high spin site is part of an unusual 4Fe–4S cluster with one Fe
2.5+ –Fe
2.5+ pair
having a spin of 9/2 and another more valence trapped “Fe
2+ –Fe
3+ ” pair having also
a spin of 9/2. An antiparallel spin arrangement than causes the diamagnetism of the
[4Fe–4S]
2+ cluster of LytB.
When the chemical substrate HMBP is added to the LytB protein the Mössbauer spectrum chances significantly (Fig. 4.25). An analysis of the data displayed
in Fig. 4.25b indicates that only the doublet representing the special iron(II) site is