Download Membrane Transport

Chapter 11
Membranes: Transport
Part 2
Learning Goals
To KNOW:
- mechanisms of molecular transport in and out of cells.
- transport kinetics (really easy after Chapter 6!)
- specific transporters: Ca++ transporter, Na+/K+
transporter, glucose transport in gut epithelial cells, P,V
and F-type ATPases, lactose transport in bacteria
- aquaporins
Membrane Transport
Energetics of Diffusion Transport
EOC Problem 15 is all about tryptophan and indole permeability,
review their structure (Chapter 3) or you already know it !!
Glut1 Transporter (Erythrocyte Glucose Transporter)
Each α-helix has a Non Polar Side and Polar Side
Polar Groups Define the Transporter Pore
EOC Problem 11 deals with evidence on the location of
membrane proteins. A good class activity.
Transport Kinetics
vo = Vmax [Sout] / (Kt + [Sout])
kt is the same as kcat…. and Kt is Km of transport
Glucose Transport Model
Tissues where Expressed
Kt (mM)
Role
Insulin Increases Number of Glucose Transporters
Related to this is membrane self-sealing: Check out EOC
Problem 12
Chloride Transporter Linked to CO2 Exchange
Secondary Transporters
Secondary Transporters = use a chemical gradient + electrical gradient.
Two Types of Active Transport
S1 is usually H+ or Na+
Therefore Outside Cell Membrane (Na+) or Mitochondria
Membrane (H+) there is:
high concentration of S1 and lower in the cytoplasm or
mitochondrial matrix.
On the outside: higher chemical conc. + electrical charge
…….these are 2 energetic components.
This is called either the Proton
Motive Force
Sodium Motive Force
or
EOC Problem 10: Energetics of symports.
Ca++ Transporter
in Sarcoplasmic
Reticulum
Ca++ Transporter
works like a little
motor
General Structure P-type
ATPases
P-type Na+K+
ATPase
Inhibitor of P-type ATPases which become
Phosphorylated in the Transport Cycle
P-type Na+/K+
ATPase Maintains
the Na+ - K+
disequilibrium
If you add up just the
sodium and potassium
concentrations…it
doesn’t seem right, but it
is because the
concentrations of Cl-,
Mg++, Ca++ and all the
other weak acids are all
part of the overall
electrochemicalgradient.
Ouabain Binds to the Open - Outside form of Na+K+
ATPase..and hold it there.
Arrow Poison
V-type
and
F-type ATPase
F-type ATPase Is Reversible and Can Make
ATP
ABC Transporters in E. coli
Nucleotide Binding Domains
Lipid-a Flippase
Vit-B12 Transporter
CFTR (Chloride Transporter)
Cystic Fibrosis Transmembrane
conductance Regulator
Cystic Fibrosis Patients Can’t Clear Bacteria
in Bronchia-Trachea
Cystic Fibrosis – Research at FIU in Dr. Kalai Mathee’s Lab
CFTR In Action
See Box 11-2 Page 415 For More
Proton Motive Force
Lactose Transporter in Two Forms
12 Transmembrane Helices
Arg and Glu in Green, Lactose in Red
Transporters Need to be at the Right Side of a Cell
How Are Transporters Regulated?
1st Crystal Structure of the E. coli Methionine ABC Transporter
Fig. 1. (A) ABC transporter MetNI consists of four subunits: two membrane-spanning MetI subunits (green
and pink) and two MetN ABC subunits (purple and tan)
Structure B is A in a 90o Turn
TMD – transmembrane domain, NBD – Nucleotide binding domain, C-2 Methionine binding domain
C-2 Domain of Met-Transporter
Methoinine – gold structures. When bound, Met
inhibits the NDB as an ATPase, Ki ~ 30 µM
Ref: Kadaba, Kaiser, Johnson, Lee and Rees. 2008. The high affinity E. coli methionine
ABC transporter: structure and allosteric regulation. SCIENCE 231:250-253
Ionophores (Valinomycin) Disrupt Ion Gradients
K+
Discovered Aquaporins (AQP) – Water Transport
Aquaporins
EOC Problem 16 is a classic aquaporin water flow kinetics
problem.
Things to Know
1. Membrane transport kinetics: KT and kt
2. Amino acids in transmembrane domain of transporters.
3. Primary and Secondary Transporters.
4. Transporters as motors.
5. PMF.
6. Cell location of transporters: intestinal cell model.
7. Transporter regulation
8. Aquaporins
9. EOC Problems : 10-13, 15, 16, 22 .
Model for EOC
Problem 22
Fill in the Amino
Acids with Single
Letter Code: What
does it tell you?
Val-Asp-Arg-Val-Phe-Ser-Asn-Val-Cys-Thr-His-Leu-Lys-Thr-Leu-Gln-Asp-Lys