20
ANNOUNCEMENTS
1. LECTURE HOMEWORK ASSIGNMENT NOT AS IN LG FOR THIS WEEK! INSTEAD: TEXT pp. 343-363
& 371 - 389; PROBLEMS Ch.10#7,16 & Ch.11#4,15 AND LG 32-34
2. PYMOL #6, CHYMOTRYPSIN (WILL APPEAR ON MIDTERM EXAM)
3. REMINDER: NO QUIZ NEXT WED 10/19
4. MEET FRI 10/14 2:55PM COMSTOCK B108. HOW TO STUDY FOR THIS COURSE. NO
DISCUSSION OF MATERIAL ON MIDTERM EXAM (THAT DISCUSSION MONDAY, IN CLASS);
DISCUSSION WILL BE POSTED AS AN ADDENDUM TO FRIDAY LECTURE.
5. MIDTERM ROOMS ROCKEFELLER: A - M IN SCHWARTZ AUD.; N - Z IN 203 (AUD. B)
LECTURE OF FRIDAY 10/7
1. ALLOSTERIC REGULATION OF AN ENZYME: ASPARTATE CARBAMOYL TRANSFERASE,
ENZYME THAT CAN DO R
T
2. COVALENT REGULATION OF AN ENZYME: CHYMOTRYPSINOGEN
CHYMOTRYPSIN
3. GENERAL MEMBRANE PROPERTIES; TYPES OF LIPID BILAYER PHASES
TODAY
LIPIDS PROPERTIES AND CHEMICAL RXNS
PROTEINS IN BIOMEMBRANES
FUSION OF MEMBRANES
ANCIENT AS THE FIRST
CELL!
BIOMEMBRANES: GENERAL PROPERTIES
COMPOSITION BY MASS:
30-70% PROTEIN 30-70% LIPID
~5% CARBO
ALWAYS COVALENTLY
ATTACHED TO PROTEIN OR LIPID
WHAT IS A LIPID?
WATER-INSOLUBLE,
OIL-LIKE BIOMOLECULE
IN BIOMEMBRANES, LIPIDS
ARE AMPHIPHILIC
BOTH
USED HERE AS
JARGON
NOTICE ASYMMETRY
IN THE OUTER
LEAFLET,
Nucleus
COMPARED WITH
THE INNER LEAFLET: Cytosol
DIFF. LIPIDS, DIFF.
PROTEINS
ASYMMETRY OF LIPIDS HARD TO STUDY
LOVE
i.e. BIOMEMBRANE LIPIDS
HAVE A POLAR PART AND
A NONPOLAR PART
THE NONPOLAR PART
GETS OUT OF WATER
BIOMEMBRANE H2O, O2, N2, CO2, EtO
PERMEABLE TO STEROLS,
IONS, SUGARS, AA,
NOT PERMEABLE TO PROTEINS,
NUCLEOTIDES
3 KEY TYPES OF LIPID
BILAYER PHASES
1. LIQUID
ACYL CHAINS
WIGGLING;
DISORDERED;
PROTEINS &
LIPIDS MOVE;
2-DIMENSIONAL STATE OF MATTER!
TYPICAL FOR
UNSATURATED
ACYL CHAINS
2. SOLID
WATCH VIDEO (ON YOUR CD):
"BIOMEMBRANES"
3. LIQUIDORDERED
ACYL CHAINS
STRAIGHT, BUT
PROTEINS & LIPIDS
MOVE; MUCH OF
PLASMA MEMBRANE
LIKE THIS. IT IS
INDUCED BY
CHOLESTEROL.
CALLED "RAFT PHASE"
ACYL CHAINS STRAIGHT;
RIGID; PROTEINS & LIPIDS
FIXED IN PLACE; VERY
LITTLE OF BIOMEMBRANE
LIKE THIS. DIFFUSION RATE
1000x SLOWER THAN LIQUID
DO REAL BIOMEMBRANES HAVE
COEXISTING LIQUID AND LIQUIDORDERED PHASES?!
THE PHASE STATE OF
BIOMEMBRANES: ACTIVE
RESEARCH!
COEXISTING PHASES IN THE PLASMA MEMBRANE?
ARTIFICIAL GIANT BILAYER SPHERES, STAINED WITH FLUORESCENT DYES,
IMAGED USING A CONFOCAL FLUORESCENCE MICROSCOPE
COEXISTING LIQUID + SOLID
COEXISTING LIQUID + LIQUID-ORDERED
THESE MEMBRANES ARE ARTIFICIAL, CHEMICALLY SIMPLE MODEL MIXTURES
THE SIZE SCALE OF THE ABOVE MODEL PHASE DOMAINS IS ~ 1 - 10 MICRONS
IN REAL BIOMEMBRANES, ANY COEXISTING PHASES ARE SMALLER THAN ~ 0.3 MICRON
100s OF DIFFERENT
KINDS! WHY SO MANY?!
TYPES OF FATTY ACYL CHAINS FOUND IN
BIOMEMBRANES
FATTY ACID
C
SYSTEM FOR C=C
EICOSATETRAENOATE
UNSATURATION IS KEY FOR KEEPING BILAYER LIQUID
BUT REASON FOR MULTIPLE UNSATURATION IS UNKNOWN
REASON FOR DIFFERENT CHAIN LENGTHS IS UNKNOWN
NOT A FA! MOST ABUNDANT
LIPID IN MAMMALIAN
PLASMA MEMBRANES
COMPARE C18:0 WITH C18:1. DOUBLE
BOND DISRUPTS CHAIN PACKING
OLEATE, C18:1
MEMBRANE NOT SOLID!
FAVORS LIQUID BILAYER
STEARATE, C18:0
FAVORS SOLID BILAYER
CHOLESTEROL
STRUCTURE OF SOME BILAYER-FORMING LIPIDS
ONE COMMON TYPE
1
GLYCERO2
PHOSPHOLIPID
OTHER COMMON
TYPES ARE NOT 3
X
FORMED FROM
GLYCEROL
"HEADGROUP"
NAME OF
GLYCEROPHOSPHOLIPID
LIPID
NAME OF X
_ _FORMULA OF X
_
ABBREV.
ABBREV.
PA
TWO CHAINS IS KEY:
1. INSOLUBLE
2. CROSS-SECTIONAL
AREA OF 2 CHAINS
MATCHES CROSSSECTIONAL AREA OF
HEADGROUP
MEMBRANE IF FLAT!
WHAT CHAIN AREA MUCH
GREATER THAN HEADGROUP
NET
A
CHARGE, REA?
POLAR NONPOLAR
pH 7
-1 SOME
PE
0
PC
PS
PG
H
PI
H
_
HEADGROUPS
(INCLUDING
PACKING
YIELDS
CURVED
MEMBRANE
THE PO4-) ARE
0 ZWITTERIONS;
SOME HEAD-1 GROUPS _
HAVE NET BUT IF CROSS-SECTION
NEGATIVE OF HEADGROUP AND
-1 CHARGE _ CHAINS ARE MATCHED:
PACKING
HEADGROUP
YIELDS
CHARGE & TYPE,
FLAT
CHAIN LENGTH, AND
MEMBRANE
UNSAT. ALL
-1
CONTROL PHASES
AND BINDING TO
PROTEINS
PHOSPHOLIPASES
HYDROLYZE PHOSPHOLIPIDS: PL + H2O
BIOMEMBRANE NOT "JUST" PERMEABILITY
BARRIER OR MILIEU FOR CERTAIN PROTEINS:
IT IS A CHEMICAL FACTORY!
PL HYDROLYSIS OCCURS AS
ONE PART OF "SIGNALING", e.g.
PAIN;
INFLAMMATION;
IMMUNE RESPONSE;
HAPPY OR SAD;
GROWTH
H
+
H
PRODUCT-1 + PRODUCT-2
O
H2
PHOSPHOLIPASE A2
+
LYSO-PC
DIACYLGLYCEROL
+
FATTY ACID
H
2O
+
CHOLINE
PHOSPHATE
PHOSPHOLIPASE C
PLC
PLA2
+ H 2O
H
EXAMPLE OF
PHOSPHATIDYLCHOLINE
+ H20
EXAMPLE OF
SPHINGOMYELIN
H
CHOLINE
CERAMIDE + PHOSPHATE
SPHINGOMYELINASE
CHOLINE + PHOSPHATIDIC ACID
PHOSPHOLIPASE D
PLD
PROTEINS IN BIOMEMBRANES
1/3 OF ALL PROTEINS ARE IN MEMBRANES
PROTEIN
LINKER
TYPES OF MEMBRANE ASSOCIATION
1. SINGLE -HELIX ~ 20-25AA, MOSTLY NONPOLAR. CAN HAVE C14:0 OR C16:0 ANCHOR
2. MULTIPLE -HELICES UP TO 14 HELICES FOR ONE PROTEIN; 7 OR 12 HELIX SUPERFAMILIES; ONLY OUTSIDE OF HELICES NONPOLAR. INSIDE MIGHT BE VERY POLAR
3. TWO OR MORE HYDROCARBON CHAINS IF ONLY ONE CHAIN, BINDING IS REVERSIBLE
4. GLYCOSYL PHOSPHATIDYLINOSITOL, GPI MEMBRANE ANCHOR IS PI BUT IT IS
PI.
UNKNOWN WHY CARBOHYDRATE LINKERS TO THE PROTEINS ARE NEEDED.
CARBOHYDRATE
5. INDIRECT ASSOCIATION BY BINDING TO ANOTHER PROTEIN OR MEMBRANE SURFACE
THESE PROTEINS PERIPHERAL; NOT SO DIFFICULT TO REMOVE FROM MEMBRANE
6. -BARREL NOT AS COMMON AS THE OTHER TYPES OF MEMBRANE ASSOCIATION
A "REAL" MEMBRANE, SIMPLIFIED PICTURE: THE RED BLOOD CELL MEMBRANE
RBC HAS FLEXIBLE CYTOSKELETON
ON INNER (CYTOSOLIC) SURFACE
REAL BIOMEMBRANE HAS
ASYMMETRY OF BOTH PROTEINS
AND LIPIDS
DIFFERENT IN
ANKYRIN EACH HALF
OF BILAYER
ACTIN
TROPOMYOSIN
SPECTRIN
INSIDE CELL
OUTSIDE CELL
12 -HELICES. FUNCTION:
EXCHANGE OF CO2=
Cl-
ANION CHANNEL
FUNCTION
UNKNOWN
BUT MALARIAL
GLYCOPHORIN A PARASITE
BINDS HERE!
WHAT DO CELL MEMBRANES REALLY LOOK LIKE?
A WELL-STUDIED CASE, THE SYNAPTOSOMAL VESICLE FROM A NERVE CELL
HERE, WE KNOW EVERY PROTEIN, BUT LITTLE ABOUT THE LIPID BILAYER!
A LOOK AT SOME MEMBRANE CHANNEL PROTEINS
POLAR AND CHARGED AA INSIDE CHANNEL
NONPOLAR AA IN CONTACT WITH NONPOLAR LIPID
K+ CHANNEL
Cl- CHANNEL
Ca2+ - ATPase
Na+ - COUPLED GLU
TRANSPORTER
MANY PROTEINS ARE MEMBRANE PROTEINS: ~ 1/3 OF ALL!
e.g. ALL ION CHANNELS; ALL MEMBRANE TRANSPORT PROTEINS FOR AMINO ACIDS,
NUCLEOTIDES, SUGARS; MOST HORMONE RECEPTORS
BUT FINDING STRUCTURE?! DIFFICULT TO GROW CRYSTALS OF MEMBRANE PROTEINS
MUCH PROGRESS IN PAST ~ 10 YEARS
CURRENT ACTIVE RESEARCH: WHAT GOES WRONG WITH CHANNELS IN DISEASE? e.g.
CYSTIC FIBROSIS; HOW DO HORMONE RECEPTORS TRANSMIT SIGNALS FROM OUTSIDE
TO INSIDE THE CELL?
DIFFERENT NERVE-MUSCLE SYNAPSE, FUSION OF"LIFE OF A VESICLE"
SHOWING TWO BIOMEMBRANES
TYPES OF
PRE-SYNAPTIC VESICLES IN A NERVE CELL, ~ 50 NM DIAMETER
FUSION, OR
REVERSE:
CARTOON: FUSION AT THE MOLECULAR LEVEL?
TWO BILAYERS MUST APPROACH CLOSELY
THEN, SOMEHOW, THE WATER LAYER MUST
BE REMOVED. MANY DETAILS UNKNOWN!
IN MANY CASES, FORMATION OF COILED
COILS OF -HELICES IS THE DRIVING FORCE
DETAILS OF LIPID BEHAVIOR DURING FUSION
ARE UNKNOWN