Involvement of Lysine and Tryptophan Side-Chains in the Biotin–Avidin Interaction

✍ Scribed by A. Torreggiani; C. Fagnano; G. Fini

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 284 KB
• Volume: 28
• Category: Article
• ISSN: 0377-0486
• DOI: 10.1002/(sici)1097-4555(199701)28:1<23::aid-jrs58>3.0.co;2-p

✦ Synopsis

The biotin-1,4-diaminobutane (Bio-Put), biotin-tryptophan (Bio-Trp) and biotin-3-methylindole (Bio-Sct) systems were investigated by means of Raman spectroscopy. The interaction with Put renders the polar resonance forms of Bio more stabilized. One group of Put is protonated by the COOH group of Bio and an electrostatic NH 2 interaction between the negatively charged carboxylate group and the protonated amino group takes place. As far as the Bio-Trp and Bio-Sct systems are concerned, the Raman spectra indicate that Trp and Sct are not able to form stable complexes with Bio, and speciÐc interactions between Bio and the indolic ring do not occur. The Raman results indicate that the participation of the ureido group of Bio in an extended hydrogen bond network greatly contributes to the stabilization of the complex with proteins. These speciÐc interactions favour the dipolar resonance forms of Bio which give rise to the formation of strong H-bonds with the protein. The Bio molecule is arranged in the active site in such a way that its carboxylic group orients towards a Lys residue, undergoing an ion-pair interaction with the amino group of Lys ; however, this interaction appears to play a lesser role than that with the ureido ring. In spite of the many experimental results that have indicated the direct involvement of Trp in the formation of the Bio-avidin complex, none of the Trp residues binds the Bio molecule. The indolic rings probably interact with Bio via hydrophobic or charge-transfer forces, and are involved in the construction of the hydrophobic box in which Bio resides.