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2008 ; 17
(12
): 2059-69
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Structural and biochemical studies of TREX1 inhibition by metals Identification
of a new active histidine conserved in DEDDh exonucleases
#MMPMID18780819
Brucet M
; Querol-Audí J
; Bertlik K
; Lloberas J
; Fita I
; Celada A
Protein Sci
2008[Dec]; 17
(12
): 2059-69
PMID18780819
show ga
TREX1 is the major exonuclease in mammalian cells, exhibiting the highest level
of activity with a 3'-->5' activity. This exonuclease is responsible in humans
for Aicardi-Goutičres syndrome and for an autosomal dominant retinal vasculopathy
with cerebral leukodystrophy. In addition, this enzyme is associated with
systemic lupus erythematosus. TREX1 belongs to the exonuclease DEDDh family,
whose members display low levels of sequence identity, while possessing a common
fold and active site organization. For these exonucleases, a catalytic mechanism
has been proposed that involves two divalent metal ions bound to the DEDD motif.
Here we studied the interaction of TREX1 with the monovalent cations lithium and
sodium. We demonstrate that these metals inhibit the exonucleolytic activity of
TREX1, as measured by the classical gel method, as well as by a new technique
developed for monitoring the real-time exonuclease reaction. The X-ray structures
of the enzyme in complex with these two cations and with a nucleotide, a product
of the exonuclease reaction, were determined at 2.1 A and 2.3 A, respectively. A
comparison with the structures of the active complexes (in the presence of
magnesium or manganese) explains that the inhibition mechanism is caused by the
noncatalytic metals competing with distinct affinities for the two metal-binding
sites and inducing subtle rearrangements in active centers. Our analysis also
reveals that a histidine residue (His124), highly conserved in the DEDDh family,
is involved in the activity of TREX1, as confirmed by mutational studies. Our
results shed further light on the mechanism of activity of the DEDEh family of
exonucleases.