Guisheng Zeng*, Bo Huang*, Suat Peng Neo, Junxia Wang, and Mingjie
*: co-first authors .
Pan1p plays essential roles in both actin and endocytosis in yeast.
It interacts with, and regulates the function of, multiple endocytic
proteins and actin assembly machinery. Phosphorylation of Pan1p
by the kinase Prk1p down-regulates its activity, resulting in disassembly
of the endocytic vesicle coat complex and termination of vesicle-associated
actin polymerization. In this study, we focus on the mechanism that
acts to release Pan1p from phosphorylation inhibition. We show that
Pan1p is dephosphorylated by the phosphatase Glc7p, and the dephosphorylation
is dependent on the Glc7p-targeting protein Scd5p, which itself
is a phosphorylation target of Prk1p. Scd5p links Glc7p to Pan1p
in two ways: directly by interacting with Pan1p and indirectly by
interacting with the Pan1p-binding protein End3p. Depletion of Glc7p
from the cells causes defects in cell growth, actin organization
and endocytosis, all of which can be partially suppressed by deletion
of the PRK1 gene. These results suggest that Glc7p antagonizes the
activity of the Prk1p kinase in regulating the functions of Pan1p
and possibly other actin- and endocytosis-related proteins.
Published in The EMBO Journal. Published online 29 November 2007.
Pan1p: An actin director of endocytosis
Bo Huang, Mingjie Cai.
The yeast protein Pan1p plays a key role in actin-driven endocytosis.
The molecular architecture enables the protein to perform multivalent
tasks. First, Pan1p acts as a central scaffold for assembly of coat
complex at the endocytic sites through its binding to multiple endocytic
proteins. Secondly, Pan1p is also required for normal actin cytoskeleton
organization and dynamics at the cell cortex. It is capable of F-actin
binding and promoting the Arp2/3-mediated actin nucleation via its
WH2 and acid domains. Pan1p, therefore, is responsible for the mechanism
of coupling the vesicle coat to actin network in the early steps
of internalization. The function of Pan1p is under a negative regulation
by the kinase Prk1p. Phosphorylation of Pan1p by Prk1p results in
disassembly of the coat complex and dissociation of the vesicle
from actin meshwork after internalization. The phosphorylation of
Pan1p is possibly reversed by the type 1 phosphatase Glc7p, which
will allow Pan1p to be reused for coat assembly in the next round