Dk. Eggers et Js. Valentine, Molecular confinement influences protein structure and enhances thermal protein stability, PROTEIN SCI, 10(2), 2001, pp. 250-261
The sol-gel method of encapsulating proteins in a silica matrix was investi
gated as a potential experimental system for testing the effects of molecul
ar confinement on the structure and stability of proteins. We demonstrate t
hat silica entrapment (1) is fully compatible with structure analysis by ci
rcular dichroism, (2) allows conformational studies in contact with solvent
s that would otherwise promote aggregation in solution, and (3) generally e
nhances thermal protein stability. Lysozyme, oc-lactalbumin, and metmyoglob
in retained native-like solution structures following sol-gel encapsulation
, but apomyoglobin was found to be largely unfolded within the silica matri
x under control buffer conditions. The secondary structure of encapsulated
apomyoglobin was unaltered by changes in pH and ionic strength of KCl. Intr
iguingly, the addition of other neutral salts resulted in an increase in th
e cr-helical content of encapsulated apomyoglobin in accordance with the Ho
fmeister ion series. We hypothesize that protein conformation is influenced
directly by the properties of confined water in the pores of the silica. F
urther work is needed to differentiate the steric effects of the silica mat
rix from the solvent effects of confined water on protein structure and to
determine the extent to which this experimental system mimics the effects o
f crowding and confinement on the function of macromolecules in vivo.