Transcript Mitochondrial permeability transition pore

Mitochondrial
Permeability Transition
Pore
Gao Qin
 Structure
of MPTP
 Causes
and consequences of
MPTP opening
 Effectors
of MPTP
In 1976, Hunter and Haworth first
characterized the mitochondrial permeability
transition in beef heart mitochondria.
 In 1987, Martin Crompton et al. implied that
the pore is a unique molecular entity that
allows the passage of any molecule of
<1500daltons across the inner mitochondrial
membrane.

Models of MPTP structure

Mitochondrial permeability
transition pore (MPTP) is a
non-specific pore which
spans the inner and outer
membrane.

Two hypotheses about MPTP
structure
The first:
Three core components:
 VDAC (voltage-dependent anion
channel)
 ANT
(adenine nucleotide translocator)
 CypD (cyclophilin D) exhibits peptidyl-prolyl
cis-trans isomerase(PIPase) activity.
Two conformations of ANT

According to ATP/ADP-binding site
m-conformation: on the matrix side of the
inner membrane
c-conformation: on the cytoplasmic side
Atr
Ca
The second:
Misfolding and clustering of mitochondrial
membrane proteins and regulated by
chaperones.
Types of MPTP
MPTP has two open conductance modes:
Regulated and unregulated
 Regulated MPTP opening requires several
inducers and the loading of Ca2+ into matrix
space and is inhibited by Ca2+ chelators,
Mg2+,and cyclosporin A (CsA).

Types of MPTP

Unregulated MPTP opening occurs with
high concentration of various inducers. It is
Ca2+-independent and insensitive to Ca2+
chelators, Mg2+,and CsA.
Opening of regulated and unregulated PT pores by HgCl2. After 2-3 min pre-incubation, 5 micromol/L HgCl2
plus 50 micromol/LCaCl2 (A), 20 micromol/L HgCl2 (B)were added in rat liver mitochondria (0.5 mg
protein/ml). From the beginning of the incubations, 1micromol/L CsA (traces b), 0.5 millimol/L EGTA
(traces c), or 5 millimol/L MgCl2 (traces d) was present or no additions were made (traces a).
D
Causes of MPTP opening
Mitochondrial calcium overload
 Oxidative stress
 Adenine nucleotide depletion
 Mitochondrial depolarization
 Elevated phosphate concentration

Consquences of MPTP opening
MPTP opening
small molecular
across
MPTP freely
mitochondria swell
mitochondria swell and
and outer membrane
outer membrane rupture
rupture
protein release
(eg. Cytochrome c)
proton enter into mitochondria
proton translocate ATPase
hydrolyze ATP
Effectors of MPTP

There are many
effectors influencing
MPTP.

They bond to
various sites.
Effect via change in
CyP-D binding to the
ANT
Activator
Oxidative stress
Increased matrix
volume
Inhibitor
CsA and some
analogues
SfA (inhibits PPIase
activity of CyP-D but
not binding)
Effect via change in
nucleotide binding to the
ANT
Direct effect on
Ca2+binding to the
ANT
Oxidative stress
‘‘c’’ conformation of ANT
(atractyloside)
Adenine nucleotide
depletion
High matrix [Pi] and [PPi]
Depolarization
High pH
Increase membrane
potential
“m’’conformation of ANT
(bongkrekic acid)
Low pH
Mg2+, Mn2+,
Sr2+, Ba2+
Proposed scheme for the mechanism of pore opening
Normal
Impermeable
State
Cytosol
Pathological
Non-specific
Pore
ADP
Adenine
nucleotide
translocase
ATP
Matrix
Ca2+
Ca
Triggered by low
[Ca2+]
Inhibited by [Mg2+], low pH,
adenine nucleotides
X
Cyclophilin D
Cyclosporin A
Impermeable
State
Activated by oxidative stress
which decrease ADP/ATP binding
ADP
ATP
SfA
Binding increased by oxidative stress.
Cyp-D binding increases sensitivity to
[Ca2+].
Sanglifehrin A is a
novel immunosuppressant that
binds to CyP-D
and inhibits its
PPIase activity
MPTP opens during reperfusion
but not ischemia

In ischemia phase, many factors which can induce
MPTP opening is developed, but the pH is
low(<7) , MPTP will not open

Upon reperfusion, mitochondria are again able to
respire and generate a membrane potential to
drive ATP synthesis ,pH can recover , while
inducers are also present, so MPTP opens.