Tryptophan fluorescence in the Bacillus subtilis phototropin-related protein YtvA as a marker of interdomain interaction.
The Bacillus subtilis protein YtvA, related to plant phototropins (phot), binds flavin mononucleotide (FMN) within the N-terminal light, oxygen and voltage (LOV) domain. The blue light-triggered photocycle of YtvA and phot involves the reversible formation of a covalent photoadduct between FMN and a cysteine (cys) residue. YtvA contains a single tryptophan, W103, localized on the LOV domain and conserved in all phot-LOV domains. In this study, we show that the fluorescence parameters of W103 in YtvA-LOV are markedly different from those observed in the full-length YtvA. The fluorescence quantum yields are ca 0.03 and 0.08, respectively. In YtvA-LOV, the maximum is redshifted (ca 345 vs 335 nm) and the average fluorescence lifetime shorter (2.7 vs 4.7 ns). These data indicate that W103 is located in a site of tight contact between the two domains of YtvA. In the FMN-cys adduct, selective excitation of W103 at 295 nm results in minimal changes of the fluorescence parameters with respect to the dark state. On 280 nm excitation, however, there is a detectable decrease in the fluorescence emitted from tyrosines, with concomitant increase in W103 fluorescence. This effect is reversible in the dark and might arise from a light-regulated energy transfer process from a yet unidentified tyrosine to W103.
Losi
Aba
A
Department of Physics, University of Parma, Parco Area della Scienze 7/A, 43100 Parma, Italy. losia@fis.unipr.it
Ternelli
Elena
E
Gärtner
Wolfgang
W
D001412:Bacillus subtilis / Q000502:physiology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000528:radiation effects; D056931:Cryptochromes; D005420:Flavoproteins / Q000737:chemistry* / Q000528:radiation effects; D007700:Kinetics; D013050:Spectrometry, Fluorescence; D014364:Tryptophan
D001426:Bacterial Proteins; D056931:Cryptochromes; D005420:Flavoproteins; D014364:Tryptophan