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

Dephosphorylation of keratin intermediate filaments (IF) in livers from eth anol-fed rats relative to controls occurs concurrently with a reorganizatio n 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 ker atin 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 C-13 nuclear magnetic resonanc e (NMR). Keratin IF were isolated from livers of control rats and from live rs of rats that had ethanol included in their feed for 6-40 weeks. A signif icant decrease in the intensity of the CD spectrum of keratin IF from liver s of ethanol-treated animals, relative to controls, was observed. These dat a suggested either that a change in conformation or an increase in conforma tional motility in the keratin IF from ethanol-treated animals occurred as a result of the ethanol-induced dephosphorylation. C-13 NMR data were obtai ned to distinguish between these two possibilities. An increase in resonanc e intensity of some C-13 NMR resonances was observed in the keratin IF from livers of ethanol-treated animals, relative to controls. The CD and NMR da ta 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 dynam ics detected in these experiments could be the molecular basis for the alte ration of keratin IF organization in alcoholic hepatitis. (C) 1999 Publishe d by Elsevier Science B.V. All rights reserved.