Fluorescence Enhancement of Fluorescent Unnatural Streptavidin by Binding of a Biotin Analogue with Spacer Tail and Its Application to Biotin Sensing
(a) The homo tetrameric constitution of a natural streptavidin (PDB ID: 1SWE). Subunit A was colored green, subunit B was colored yellow; to be easy to see, both subunits C and D were colored white. Biotin was colored with gray. On the other hand, Trp79, Trp108, and Trp120 in subunits A and B were colored orange, violet, and blue, respectively. Obviously the Trp120 was close to the Trp79 and the Trp108 of the neighbor subunit. (The distance from Trp120 to Trp79 of the neighbor subunit is 8.74 Å and Trp120 to Trp108 of the neighbor subunit is 6.78 Å.) (b) The chemical structure of the BFLAF.