This lecture:
• Essential Cell Biology.: chapters 11-12
• ion channels, the pumps and mechanisms relevant to
Ca, osmo- and pH regulation, also included in this
chapter of the book, will be discussed in other
lectures
• A text briefly describing the various membrane
transporters discussed in this lecture is
downloadable from our website! Together with the
- marked lecture slides this text is
required material for the tests and exam!
Cell membrane, transport
~50 membrane proteins
mutation
altered morphology
Figure 4. Red cell morphology. Hereditary
spherocytosis (HS; top panel); nonhemolytic
hereditary elliptocytosis (HE; middle panel);
elliptocytes, poikilocytes, and fragmented red cells in
hemolytic HE (bottom panel). BLOOD, 2008, 112(10)
Membrane transport
→ Membrane
– artificial
– real
→ Energetics
→ Number of transported
substances/direction of
transport
– uniport
– symport, antiport
– passive
– active
→ Transported
substance
– hydrophylic
– hydrophobic
Real membranes: passive and active transport
see
previous
slide
Active transport
Carrier-mediated - passive - transport
uniport
ionophore
Valinomycin (ionophore)
Main categories of active transport
Secondary active
transporters, carriers
P
V F
Na/K
ABC
Pgp,etc
vacuolar
symport antiport
mitochondrial
Intestinal glucose
transport
Intestinal glucose transport
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/sympo.htm
Categories of transport according to
solubility of
„S”:
A. hydrophylic substrates
B. hydrophobic substrates
Cm
R  aq  1
C
Transport of hydrophobic molecules
• Passive
– R (lipid / water partition coeff.)
– i.c. partition - Henderson-Hasselbach eq.
• Active
pH = pK + log(M/M+)
– ABC (ATP binding casette) transporters
• pump
• channel
• regulator
– Other transporters
•
Passive diffusion is governed by the lipid-water partition coefficient and its pH
dependence (expressed by the Henderson-Hasselbach relationship):
concentration
reached in
membrane
/efficiency
http://molinterv.aspetjournals.org/cgi/content/full/1/5/258
Partition coefficient may be pH-dependent consequences
R-NH3+
R-NH2
R-NH2
lysosome
pH ≈ 5
R-NH3+
cytoplasm
pH ≈ 7
Membrane transport
→ Energetics
→ Membrane
– artificial
– real
→ Number of
transported substances
– uniporter
– symporter, antiporter
– Passive (simple
diffusion, also through
channels, or facilitated,
uniport-mediated diff.)
– Active (coupled or
pumped)
→ Transported
substance
– hydrophylic
– hydrophobic
General structure of ABC transporters
TM
cell membrane
NBD
TM
– 2 transmembrane domains (TM)
– 2 nucleotide binding domains
(= NBD = ATP binding domain,
the „engine” that energizes 3 kinds
of activities, see a,b,c on next slide)
NBD
ABC: ATP-Binding Cassette
Most important ABC transporters
•
•
•
•
•
•
Drug transporters in primitive cells
MDR 1 Pgp
PC “flippase”
CFTR
TAP
(a) pump
SUR
(b) channel
(c) regulator
(a)
(a)
(a)
(b,c)
(a)
(c)
The lecture covered the material up to this
point. The rest of the slides are to be
discussed in the seminar. Before the
seminar, the students are expected to read
the extra material (text) what can be
downloaded from our website.
Drug transporters in primitive cells
• Plasmodium falciparum (malaria): chloroquin resistence
• Drug transporters in the bacterial (inner, cytoplasmic)
membrane:
– Specific for antibiotic produced by the same cell
– Multidrug transporters
"He that will not apply new remedies, must expect new evils."
Francis Bacon (1561-1626); English philosopher, essayist, statesman.
Drug transporters in prokaryotes
See also
Lodish, Fig.
15-15
Alberts, Fig.
11-17
Drug transporters in human
cells: e.g. mdr1 gene coded
P-glycoprotein (also called
Pgp or ABCB1)
P-glycoprotein
coded by the mdr1 gene
-Structure:
2x6 transmembrane domain,
2 ABC motif („engine”)
-Expression:
adrenal glands, intestines, pancreas, BBB,
cancer cell surfaces
-Substrates:
endogeneous:
exogeneous:
-Knock-out:
-Mechanism:
-Significance:
cholesterol ?
xenobiotics, drugs, “reversing agents”
BBB insufficiency
membrane → aqeous phase
cancer chemotherapy
Phosphatidyl choline (PC) flippase (MDR2,
also called ABCB4)
-Expression: hepatocytes, apical
membrane
-Substrates: endogeneous: PC
-Mechanism:
PC flippase, exports PC to the outer
leaflet
to be extracted from there by the bile
acids
-Knock-out, genetic disease:
PC- depletion in bile → cholangitis,
death, progressive familial intrahepatic
cholestasis (PFIC) type 3
ABC pumps of intestines
grapefruit juice
(flavonoids)
MRP1
Pgp
ABCG2
Multi-drug transporters in the blood-brain barrier (BBB)
BBB
ABC-pumps of the liver
ABCG5/G8
cholesterol
CFTR:
(„cystic fibrosis
transmembrane
conductance regulator”):
(ATP-dependent) chloride
channel, as well as
(ATP-dependent) regulator
of certain accompanying
channels;
In its absence (genetic defect):
viscous mucus in bronchioli
Nature Cell Biology 8,
908 - 909 (2006)
TAP (oligopeptid
transzporter):
Viral and cellular proteins
decomposed to harmless oligopeptides
by proteasomes in the cytosol are
pumped into the lumen of the
endoplasmatic reticulum by TAP I/II.
The peptides, „signatures” of the
proteins they are derived from,
become complexed with MHC I
proteins and appear on the cell surface.
They are exhibited to the immune
system as a „moving exhibition”,
eliciting specific immune response
by T cells.
Alberts,
Figure 24-58
.
K+
Heterooctamer
SUR
Glucose ↑ → ATP↑ → closed state is
stabilized → depol. → insulin secr.
ATP↓ → hydrolysis → opening → hyperpol.
Vertical
heterogeneity
Asymmetric lipid
composition
PS exposure on the surface of dying
cells: eat-me signal for the
phagocytes
dynamic equilibrium between flippasesfloppases (vectorial lipid transporters) and
scramblases
The following slides are included either as
reminders, or as illustrations / reference
material
hydrophylic anaesthetic
rso
ghost
RBC
hypotonic
normotonic
iso
Model of secondary-active transport
Arteficial membranes
5-8
nm
Vesicles and MBLs
MW
SDS gelelectrophoretogramm
(SDS-PAGE)
(RBC membrane proteins)
Lateral pressure profile
„surfactants”
Q
“Scanning calorimetry”
T
T<Tm
T>Tm
Z. Cournia,
http://zarbi.chem.yale.edu/~zoe/
„mdr reversion” = „modulation”
drug
cc.i
ATP-depleted Pgp+ cells
or Pgp- cells
ATP-depleted Pgp+ cells
+ATP
t
Human NK cells readily form membrane nanotubes.
Chauveau A et al. PNAS 2010;107:5545-5550
©2010 by National Academy of Sciences