Conformation of human carbonic anhydrase II variants adsorbed to silica nanoparticles

Conformational changes of human carbonic anhydrase II (HCAII(pwt)) adsorbed on silica nanoparticles (with an average diameter of 9 Mn) have been inves tigated using differential scanning calorimetry (DSC), and in some specific cases also using circular dichroism (CD) and intrinsic tryptophan fluoresc ence. To relate the observed conformational changes to the denaturation sta bility and/or chemical properties in solution, two N-terminally truncated v ariants and two mutants of HCAII(pwt) containing specific single site mutat ions were also investigated. From the thermal transitions of HCAII(pwt) ads orbed to the nanoparticles we found that this variant forms a state that wa s distinctly different from both the native and molten globule states in so lution. No thermal transition at all was observed for any of the other vari ants adsorbed on nanoparticles. CD and intrinsic tryptophan fluorescence in dicate that these variants attain a molten globule-like state at the surfac e.