The phage shock protein (Psp) response maintains integrity of
the
inner
membrane
(IM)
in
response
to
extracytoplasmic
stress
conditions
and is widely distributed
amongst
enterobacteria
. I
ts central component
PspA
,
a member of the IM30
peripheral membrane
protein
family
, acts as
a major effector of the system
through
its direct
association with the
IM
. Under non
-
stress con
ditions PspA
also negatively regulates its own expression via
direct
interaction with the AAA+ ATPase PspF. PspA
has
a counterpart in cyanobacteria called
Vipp1
,
which is
implicated in
protection of the
thylakoid membrane
s
.
PspA’s and Vipp1’s
conserved
N
-
terminal
regions contain a putative
a
mphipathic
h
elix a (AHa) required for
membrane
binding
.
An
adjacent
amphipathic helix b (AHb)
in PspA
is required for imposing
negative control
upon
PspF
.
Here, p
urified peptides derived from the
putative AH regions o
f
PspA and Vipp1
were used to directly probe
their effector
and regulatory function
s
.
We
observed direct membrane
-
binding of
AHa
derived peptides and an accompanying change
in secondary structure from
unstructured
to
alpha
-
helical
establishing them as
bona
fide
membrane
-
sensing AH’s. The p
eptide
-
b
inding specificit
ies
and the
ir
effects on membrane
stability
depend on
membrane anionic lipid content and
stored curvature elastic
stress
,
in
agreement with
ful
l length PspA and Vipp1 protein
functionalities.
AHb
of PspA inhibited the
ATPase
activity
of PspF
demonstrating
its direct regulatory role. These findings
provide new
insight into the membrane binding and function of
PspA and Vipp1
and
establish
that
synthetic peptides can
be used to
probe
the structure
-
fu
nction of the
IM30 protein family
.