M. Moroni et D. Garland, In vitro dephosphorylation of alpha-crystallin is dependent on the state of oligomerization, BBA-PROT ST, 1546(2), 2001, pp. 282-290
Citations number
25
Categorie Soggetti
Biochemistry & Biophysics
Journal title
BIOCHIMICA ET BIOPHYSICA ACTA-PROTEIN STRUCTURE AND MOLECULAR ENZYMOLOGY
alphaA- and alphaB-crystallin, members of the small heat shock protein fami
ly, are present in lens cell extracts as large aggregates. Both alpha -crys
tallins are found partially phosphorylated. This study tests the ability of
five phosphatases (protein phosphatase PP1, PP2A, PP2B, alkaline and acid
phosphatases) to dephosphorylate aA- and alphaB-crystallin in vitro. Activi
ty of a phosphatase was dependent on the size of the aggregate. Each of the
phosphatases tested showed different specificity and efficiency towards al
phaA- and alphaB-crystallins, which depended on the oligomeric state of the
alpha -crystallin aggregate. Alkaline phosphatase dephosphorylated both al
phaA- and alphaB-crystallin. The reaction was faster when alpha -crystallin
was in a tetrameric form. PP2A dephosphorylated primarily alphaA-crystalli
n but only after the conversion of alpha -crystallin to tetramers. PPI and
PP2B did not dephosphorylate either alphaA- or alphaB-crystallins present a
s large aggregates but could not be tested on the lower molecular weight fo
rm of alphaA-crystallin. Acid phosphatase dephosphorylated both alphaA- and
alphaB-crystallin. The results suggest that an important relationship exis
ts between the structure of alpha -crystallin and its level of phosphorylat
ion in the cell. (C) 2001 Elsevier Science B.V. All rights reserved.