IBR   13079
INSTITUTO DE BIOLOGIA MOLECULAR Y CELULAR DE ROSARIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The coenzyme binding site of bacterial Ferredoxin/flavodoxin NADP(H) reductases.
Autor/es:
INMACULADA PEREZ-DORADO; JUAN. A HERMOSO; GUILLERMINA GOÑI; MILAGROS MEDINA; ANA BORTOLOTTI; NÉSTOR CARRILLO; NÉSTOR CORTEZ
Lugar:
Jaca, Spain
Reunión:
Simposio; 16th Symposiumon Flavins and Flavoproteins; 2008
Resumen:
Flavoproteins
with ferredoxin-NADP(H) reductase (FPR/FNR) activity are ubiquitous among
living organisms, participating in electron transport pathways that require
splitting of electrons between obligatory two-electron carriers (i. e.,
pyridine nucleotides) and one-electron transporters such as ferredoxin or
flavodoxin [1]. They are found in both strict and facultative anaerobes,
suggesting an ancient origin. After appearance of oxygenic photosynthesis, FPRs
were recruited into the photosynthetic electron transport chain, direction of
electron flow was reserved to favour NADP+ reduction, and an
increase in catalytic efficiency occurred to cope with the demands of the novel
metabolism [1]. Enzymes found in plastids and cyanobacteria are characterized
by an extended FAD conformation and an invariant tyrosine residue at the
C-terminus. Instead, the FPRs from eubacteria bind FAD in a bent conformation, and
the amino acid facing the flavin may be aromatic or aliphatic. To acknowledge
the distinctive features of the two reductase classes, the name FNR has been to
the plastidic/cyanobacterial enzymes, while those found in eubacteria are
termed FPRs [1].
A slower hydride
transfer rate and a weaker coenzyme binding were previously described for FPRs
when compared with their plastidic counterparts [1]. Structurally-based
aligments and model docking described herein indicate that improvement of
NADP(H) interaction was attained through stronger nucleotide binding, whereas
single turnover experiments showed that the general reaction pathway was hardly
modified. Contacts with the adenosine moiety of NADP(H) play a key role in
docking. The most remarkable difference between the two types of reductases
concerns R203 of Rhodobacter FPR,
which is replaced by a conserved tyrosine in FNRs. This tyrosine appears to be
critical for nucleotide affinity undergone by alanine mutants in Anabaena FNR [2]. Replacement of R203 by
a tyrosine would turn a possible cation-π interaction into a π- π interaction with the
adenosine, and it is likely that this substitution was one of the key steps
leading to increased catalytic competence in photosynthetic FNRs.