A model for the full-length structure of the blue light-sensing protein YtvA
from Bacillus subtilis has been determined by EPR spectroscopy, performed on
spin labels selectively inserted at amino acid positions 54, 80, 117 and 179.
Our data indicate that YtvA forms a dimer in solution and enable us, based on
the known structures of the individual domains and modelling, to propose a
three-dimensional model for the full length protein. Most importantly, this
includes the YtvA N-terminus that has so far not been identified in any
structural model. We show that our data are in agreement with the crystal
structure of an engineered LOV-domain protein, YF1, that shows the N-terminus
of the protein to be helical and to fold back in between the β-sheets of the
two LOV domains, and argue for an identical arrangement in YtvA. While we
could not detect any structural changes upon blue-light activation of the
protein, this structural model now forms an ideal basis for identifying
residues as targets for further spin labelling studies to detect potential
conformational changes upon irradiation of the protein