I" sing hot h fluorescent am! non -fluorescent hydro p ho hic probes, di valent rations (Ca2+. Mg2+. Mn2-K and Zn2+) signifuantly increase Hydrophobie exposure nn GroKI,. whereas monovalent rations (K-t- and Na+) do not. Independent of the method used, /n2+ always induced I he largeM amount ot hydrophohic surface exposure on GroEL. The binding of bis ANS to GroKL in the pre.sence of Xn2 + has a Kd approx 1 uM. a value similar to other published bis ANS dissociation constants. At higher protein concentrations, the aggregation of GroKI, in the presence of Zn2+ prevented the direct determination of the number of bis-ANS binding sites per GroEI. 11-mer. However, the iru re. a se in the bis ANS fluorescence intensity as a function of the hi1- ANS Irequemy maximum, in going from GroKI, + MnCl2 to GroEI, + X.n("l2. indicates that the quantum yield of the bis-ANS has increased. This suggests that there U an increase in the amount of hydrophobic surface exposure on GroKI.. Structural analysis of GroEI, in the presence of /u + 2. by urea denaturation. sediinenta (ion velocity, and electron microscopy, revealed thai the quaternary structure of GroKI. has a stability and morphology equivalent to unliganded GroKL. In i ont rast, t lie secondary structure of GroEL +/' Xn2+ wa.s analy/ed by circular dichroism and indicates loss in both a-helical and b-sheet etondary .structure in 1 he présente of /n2-K Tluih. our data suggest that divalent ( atioiii ( an mod nlate the amount of hydrophobic surface presented by Grol-'I.. I he influence of '/n2+ on GroKI. hydrophobic surface exposure, appear- lu be ,i distinct inieiaction than the stabili/ing effect that Mg2-f has on (iiof-'.l, (piateniary structure.
|Original language||English (US)|
|State||Published - 1997|
ASJC Scopus subject areas
- Molecular Biology