an evolutionarily conserved protein FucU (Fucose, Unknown) is a close paralogue of RbsD, with any compared pair of RbsD and FucU homologues sharing about 20% amino acid sequence identity with each other.
—so says the study “Crystal Structures of RbsD Leading to the Identification of Cytoplasmic Sugar-binding Proteins with a Novel Folding Architecture,” Min-Sung Kim, Joon Shin, Weontae Lee, Heung-Soo Lee and Byung-Ha Oh, Journal of Biological Chemistry, vol. 278, no. 30, July 25, 2003, pp. 28173–80. (Thanks to investigator Caroline Richmond for bringing this to our attention.)