PLANT PHYSIOLOGY , Vol 103, Issue 1 205-212, Copyright © 1993 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Uncoating of Clathrin-Coated Vesicles by Uncoating ATPase from Developing Peas
T. Kirsch and L. Beevers
Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019
A cytosolic uncoating ATPase (an enzyme that dissociates clathrin from
clathrin-coated vesicles in the presence of ATP) was isolated from
developing pea (Pisum sativum L.) cotyledons using chromatography on
ATP-agarose. After chromatography on phenyl Sepharose, the fraction with
uncoating activity was enriched in a doublet of 70-kD peptides. Using
chromatofocusing, it was possible to produce fractions enriched in the
upper component of the doublet of 70-kD peptides; these fractions still
retained ATP-dependent uncoating activity. In western blot analysis,
antibodies against a member of the 70-kD family of heat-shock proteins
interacted with the upper component of the doublet of the 70-kD peptides
from the phenyl Sepharose-purified fractions. On the basis of these data,
it appears that the uncoating ATPase may be a member of the 70-kD family of
heat-shock proteins. The uncoating activity removed clathrin from both pea
and bovine brain clathrin-coated vesicles. The uncoating ATPase from bovine
brain also uncoated coated vesicles from peas. Pea clathrin-coated vesicles
that were prepared by three different methods were uncoated to different
extents by the plant uncoating ATPase. Different populations of
clathrin-coated vesicles from the same preparation showed differential
sensitivity to the uncoating ATPase. Limited proteolysis of the clathrin
light chains in the protein coat abolished the susceptibility of the
clathrin-coated vesicles to the uncoating ATPase. The properties of the
uncoating ATPase isolated from developing pea cotyledons are similar to
those of uncoating ATPases previously described from mammalian and yeast
systems. It appears that despite dissimilarities in composition of the
clathrin components of the vesicles from the respective sources, uncoating
is achieved by a common mechanism.