Altering the state of phosphorylation of rat liver keratin intermediate filaments by ethanol treatment in vivo changes their structure

Abstract

Dephosphorylation of keratin intermediate filaments (IF) in livers from ethanol-fed rats relative to controls occurs concurrently with a reorganization of the distribution of IF in the cells. One possible molecular mechanism for this reorganization is a phosphorylation-induced conformational change in the keratin that propagates as a change in the polymerization of the keratin subunits. To test this hypothesis, the structure of liver keratin IF, from both control and alcohol-fed rats, was explored by circular dichroism (CD), tryptophan fluorescence quenching, and 13C nuclear magnetic resonance (NMR). Keratin IF were isolated from livers of control rats and from livers of rats that had ethanol included in their feed for 6–40 weeks. A significant decrease in the intensity of the CD spectrum of keratin IF from livers of ethanol-treated animals, relative to controls, was observed. These data suggested either that a change in conformation or an increase in conformational motility in the keratin IF from ethanol-treated animals occurred as a result of the ethanol-induced dephosphorylation. 13C NMR data were obtained to distinguish between these two possibilities. An increase in resonance intensity of some 13C NMR resonances was observed in the keratin IF from livers of ethanol-treated animals, relative to controls. The CD and NMR data were therefore consistent with an increase in conformational motility of the rod domain in these keratin IF. No significant change was observed in the quenching of tryptophan fluorescence by KI. The change in protein dynamics detected in these experiments could be the molecular basis for the alteration of keratin IF organization in alcoholic hepatitis.