download report - Istituto Pasteur

A. Boffi - Escherichia coli strains overexpressing flavohemoglobins for the production of novel compounds
quency at 1888 cm-1 (corresponding to the extremely
high RR stretching frequency at 545 cm-1) indicates
unusually strong hydrogen bonding between
CO and distal residues. On the basis of a comparison
with other truncated hemoglobins it is envisaged
that the two CO conformers are determined by specific
interactions with the TrpG8 and TyrB10
residues. Mutation of TrpG8 to Leu deeply alters
the hydrogen-bonding network giving rise mainly to
a CO conformer characterized by a Fe-CO stretching
band at 489 cm-1 and a CO stretching band at 1958
cm-1. Picosecond laser photolysis experiments carried
out on the CO bound adduct revealed dynamical
processes that take place within a few nanoseconds
after photolysis. Picosecond dynamics is largely
dominated by CO geminate rebinding and is consistent
with strong H-bonding contributions of
TyrB10 and TrpG8 to ligand stabilization. These
data indicate that the structure and dynamics of the
active site in bacterial globins is not designed to bind
reversibly oxygen, as in vertebrate hemoglobins.
Towards novel functional properties
During the course of this investigation, it has been
demonstrated that truncated hemoglobins from
Bacillus subtilis and Thermobifida fusca are endowed
with an unusual high affinity for hydrogen sulfide.
The physiological relevance of this finding has been
further demonstrated by the observation that, within
the bacterial cells, these proteins are saturated with
6
hydrogen sulfide produced in at least two metabolic
steps of the bacterial cell, namely cysteine degradation
and synthesis of iron-sulfur centers. This finding
point to a specific role of bacterial globins within
the complex and still largely ununderstood metabolism
of sulfur in bacteria. In our view, the physiological
relevance (are bacterial globin sulfide sensing
proteins?) and evolutionary perspective (are globins
evolved from sulfide binding proteins in archea?) of
this preliminary finding warrants further dedicated
research on the subject.
Selected Publications
Bonamore A, Attili A, Arenghi F, Catacchio B,
Chiancone E, Morea V, Boffi A. A novel chimera:
the "truncated hemoglobin-antibiotic monooxygenase"
from Streptomyces avermitilis. Gene 2007,
398:52-61.
Di Giulio A, Bonamore A. Globin interactions with
lipids and membranes. Methods in Enzymol. 2008,
436:239-52.
Feis A, Lapini A, Catacchio B, Brogioni S, Foggi P,
Chiancone E, Boffi A, Smulevich G. Unusually
strong H-bonding to the heme ligand and fast geminate
recombination dynamics of the carbon monoxide
complex of Bacillus subtilis truncated hemoglobin.
Biochemistry 2008, 47:902-10.