In molecular biology, the BLUF domain (sensors of blue-light using FAD) is a FAD-binding protein domain.

They are present in various proteins, primarily from bacteria, for example a BLUF domain is found at the N-terminus of the AppA protein from Rhodobacter sphaeroides.

The BLUF domain is involved in sensing blue-light (and possibly redox) using FAD and is similar to the flavin-binding PAS domains and cryptochromes.

The predicted secondary structure reveals that the BLUF domain has a novel FAD-binding fold.

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