PROFILIN--STRUCTURE/FUNCTION RELATIONSHIPS

Project: Research project

Project Details

Description

Profilin regulates the stability and distribution of filamentous actin
structures in all eukaryotic cells. This regulation is due, in part, to
the ability of profilin to bind monomeric actin and catalyze nucleotide
exchange, which can lead to an increase in filamentous actin. This
activity is modulated by binding to phosphoinositides such as PIP2, which
disrupts the profilin-actin complex. The binding of profilin to PIP2 also
inhibits the phospholipase Cg catalyzed hydrolysis of PIP2 to the second
messengers PIP3 and diacylglycerol. Thus profilin may serve to link the
organization of the actin cytoskeleton to the phosphoinositide signal
transduction pathway. The identification of profilins with different
lipid binding and nucleotide exchange activities allows for regulation
of the actin cytoskeleton.

The binding of profilin to PIP2 will likely involve the interaction of
basic surface residues with the acidic phospholipid headgroups, and may
be facilitated by a conformational rearrangement placing hydrophobic side
chains in the lipid interior. Birch pollen profilin binds actin but does
not catalyze nucleotide exchange, Suggesting that modest alterations of
profilin can confer nucleotide exchange activity. Structural information
from high resolution X-ray diffraction and solid state NMR will help to
identify residues involved in PIP2 binding and nucleotide exchange
activity. The contribution of these residues will be tested by site
directed mutagenesis and biochemical characterization. The in viva
importance of species-specific and isoform-specific lipid binding and
nucleotide exchange activities will be tested by heterologous expression
of biochemically defined profilins in yeast and mammalian cells.

These studies are likely to result in a structural mechanism for profilin
sequestration by phosphoinositides and an explanation for the isoform
specific interactions with PIP 2. The details of these interactions are
central to understanding the connection between signal transduction
pathways and cytoskeletal reorganization, and will represent the first
structural analysis of a complex containing a molecule that regulates
phosphoinositide/second messenger metabolism. The expression studies will
test the importance of specific profilin activities in vivo, and identify
species-specific differences in cytoskeletal regulatory mechanisms.
StatusFinished
Effective start/end date9/30/953/31/96

Funding

  • National Institute of General Medical Sciences

ASJC

  • Cell Biology

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