This lecture:
• Essential Cell Biology, 3rd ed.: 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
Cell membrane, transport
• + lecture notes (web pages)
~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
– passive
– active
→ Transported
substance
– hydrophylic
– hydrophobic
– uniport
– symport, antiport
Real membranes: passive and active transport
see
previous
slide
Active transport
Main categories of active transport
Carrier-mediated - passive - transport
uniport
ionophore
Secondary active
transporters, carriers
P
V F
Na/K
Valinomycin (ionophore)
vacuolar
symport antiport
Intestinal glucose
transport
ABC
Pgp,etc
mitochondrial
Intestinal glucose transport
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/sympo.htm
Transport of hydrophobic molecules
Categories of transport according to
solubility of
„S”:
• Passive
– R (lipid / water partition coeff.)
– i.c. partition - Henderson-Hasselbach eq.
A. hydrophylic substrates
pH = pK + log(M/M+)
• Active
B. hydrophobic substrates
R=
– ABC (ATP binding casette) transporters
• pump
• channel
• regulator
Cm
>1
C aq
– 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
hydrophylic anaesthetic
R-NH3+
R-NH2
R-NH2
lysosome
pH ≈ 5
R-NH3
cytoplasm
pH ≈ 7
+
General structure of ABC transporters
Membrane transport
TM
→ Energetics
→ Membrane
– artificial
– real
→ Number of
transported substances
– uniporter
– symporter, antiporter
cell membrane
– Passive (simple
diffusion, also through
channels, or facilitated,
uniport-mediated diff.)
– Active (coupled or
pumped)
→ Transported
substance
– hydrophylic
– hydrophobic
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
(a)
(a)
(a)
(b,c)
(a)
(c)
• 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.
(c) regulator
Drug transporters in prokaryotes
See also
Lodish, Fig.
15-15
Drug transporters in primitive cells
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
Phosphatidyl choline (PC) flippase (MDR2, also
called ABCB4)
-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
In normal bile the inherent toxicity of bile acids is quenched by PC. In the bile of
PFIC 3 patients bile acid monomers are toxic.
ABC pumps of intestines
grapefruit juice
(flavonoids)
MRP1
-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
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
http://en.wikipedia.org/wiki/Cystic_fib
rosis_transmembrane_conductance_re
gulator
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
.
Vertical
heterogeneity
http://en.wikipedia.org/wiki/S
ulfonylurea_receptor
K+
http://www.bio.davidson.edu/courses/Immunolo
gy/Students/spring2000/buxton/MFIP.htm
Heterooctamer
Asymmetric lipid
composition
SUR
Glucose ↑ → ATP↑ → closed state is
stabilized → depol. → insulin secr.
ATP↓ → hydrolysis → opening → hyperpol.
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
rso
ghost
RBC
hypotonic
normotonic
Model of secondary-active transport
iso
Arteficial membranes
Vesicles and MBLs
5-8
nm
MW
SDS gelelectrophoretogramm
(SDS-PAGE)
(RBC membrane proteins)
“Scanning calorimetry”
Q
Lateral pressure profile
„surfactants”
T
T<Tm
T>Tm
See also:
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
ATP
t
Human NK cells readily form membrane nanotubes.
Chauveau A et al. PNAS 2010;107:5545-5550
©2010 by National Academy of Sciences