The YtfE protein catalyzes the reduction
of NO to N2O, protecting iron–sulfur clusters from
nitrosylation. The
structure of YtfE has a two-domain architecture, with a diiron-containing
C-terminal domain linked to an N-terminal domain, in which the function
of the latter is enigmatic. Here, by using electron spin resonance
(ESR) spectroscopy, we show that YtfE exists in two conformational
states, one of which has not been reported. Under high osmotic stress,
YtfE adopts a homogeneous conformation (C state) similar to the known
crystal structure. In a regular buffer, the N-terminal domain switches
between the C state and a previously unidentified conformation (C′
state), the latter of which has more space at the domain interface
to allow the trafficking of NO molecules and thus is proposed to be
a functionally active state. The conformational switch between the
C and C′ states is pivotal for facilitating NO access to the
diiron core.
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