D. Sheluho et Sh. Ackerman, An accessible hydrophobic surface is a key element of the molecular chaperone action of Atp11p, J BIOL CHEM, 276(43), 2001, pp. 39945-39949
Atp11p is a soluble protein of mitochondria that binds unassembled beta sub
units of the F-1-ATPase and prevents them from aggregating in the matrix. I
n this report, we show that Atp11p protects the insulin B chain from aggreg
ating in vitro and therefore acts as a molecular chaperone. The chaperone a
ction of Atp11p is mediated by hydrophobic interactions. An accessible hydr
ophobic surface in Atp11p was identified with the environment-sensitive flu
orescent probe 1,1'-bis(4-anilino-5-napth-thalenesulfonic acid (bis-ANS). T
he spectral changes of bis-ANS in the presence of Atp11p indicate that the
probe binds to a nonpolar region of the protein. Furthermore, the dye quenc
hes the fluorescence of Atp11p tryptophan residues in a concentration-depen
dent manner. Although up to three molecules of bis-ANS can bind cooperative
ly to Atp11p, the binding of only one dye molecule is sufficient to virtual
ly eliminate the chaperone activity of the protein.