Download Bind to other N-CAMS

How do cells know who/what to adhere to?
11/7
Vesicle transport in a cell: why does it matter?
Extracellular matrix: Collagen, Elastin and Glycoprotein
Importance of Cell-Cell adhesion
N-CAMS: Bind to other N-CAMS
Cadherins: Bind to other cadherins
Selectins: Specialized to bind target glycoproteins
Intergrins: bind laminin of the basal lamina or fibronectin
Fibronectin
Tight junctions vs. Gap junctions
Monday Nov 14th: Your student- rough draft (four copies) are due at 8am at Dr
Wilson office (-5pts if late) so they can be check, sorted, and handed out in class
so they can be edited by fellow students (-5 pts if late).
Suggestions for term paper drafts:
Get another student or “four” to proof-read again just to double check your changes.
– If you like I can put papers in my box at office…you can put one in to be edited
and take one out to edit… do you want to voluntarily make this possible?
Be sure each item in text relates specifically to your title, feel free to delete materials..
Abstract vs. Conclusion: Make them differentthis is a tough one to do.
– Abstract: Brutal detail but short (no fluff)
– Conclusion: Nice easy to read list/review of key points + a possible sentence or
two about what the future of this sort of research will be/
Introduction: Tell the reader what topics you will discuss/teach and perhaps provide a
bit of background info if really needed/
Try to have a minimum of two different references sources cited in each paragraph. Try
for at least 3 sentences or 4 lines of text in each paragraph.
Write to remove “fluff” (it hurts to take things out that represent “neat” info) that is not
VERY specific to your paper “title”, if it does not relate to the title it probably
should be removed
With regards to content in paper you need to look for repeated items/info and please
remember: REPEAT  DELETE or rephrase/reword
Tendons consist of extracellular proteins. They are composed of
collagen fibers that are produced by fibroblasts prior to secretion
(exocytosis). Collagen “fibers” are arranged in a staggered overlapping
pattern of “fibrils”.
Disulfide bonds are critical for the cross-links that strengthen collagen! Vitamin
C (ascorbate) promotes oxidation of the sulfhydryl groups! Collagen forms a
matrix around which other cells and bone may organize.
Rubbery elastin stretches and snaps back into the original shape! It is
rich in hydrophobic charges that repel water and to help it snap “back”.
Crosslinks form between lysines link chains together. Proline allows the
protein to form many kinks in the chains. Tiny glycine is helps things fit.
Glycocalyx provides a critical carbohydrate matrix that sits between
a cell’s plasma membrane and the external environment. It also contains a
series of glycoproteins whose protein segments mediate enzymatic digestion.
Cartilage is a proteoglycan (modified ground substance) that contains varying amounts
of collagen and elastin, depending on its location and function.
The function of cartilage in a joint is to provide a hydrophyllic watery surface across
which joints can move across with minimal friction.
The function of cartilage in your ear is to be able to return to its original shape (elastin).
The function of cartilage in a vertebral disc is to resist rupture (collagen).
Why is cell-cell adhesion so important to understand?
• Migrating cells must reach, recognize, bind and stay with
their target cells, tissues and organs!
• Important implications in embryogenesis, cancer, infection,
transplantation potentials (stem cells) and disease!
• Tissue Development in the Embryo/Adult:
•
Epithelial cell to basal lamina: post burn skin
•
Neural crest cell in embryo: amputee nervous system
•
Endothelium and blood vessels: cancer
• Pathway Guidance to Lead Cells Home:
•
Chemotaxis vs. Chemo-avoidance:
•
Ligands/Receptors/Second Messengers
• N-CAMS and transmembrane adhesion molecules help mediate
binding of cells to the ECM and each other!
Embryogenesis is the development of tissues and organs. This is a
review of embryonic development in a chick, similar process also
occur in human embryos.
There are a variety of options available to cells when they seek
to bind to other cells or know if they are in the correct location.
Lets review some of the options available. Know one item that
makes each unique.
N-CAMS: Ca+Independent
• Bind to other N-CAMS
Cadherins: Ca-Dependent
• Bind to other cadherins
Selectins: don’t bind each other.
Specialized to bind target
glycoproteins
Intergrins: bind laminin of the
basal lamina or fibronectin
in the ECM or to other cells.
N-CAM: Neural Cell Adhesion Molecules
• Contain transmembrane, fibronectin
(2) and immunoglobin domains that
bind C-shapes on IG domains of
adjacent N-CAMS on other cells.
• The intracellular domains give it the
ability to alter signal transduction
inside the cell (i.e. alter transcription
translation or mitosis)
• Consider a synapse at a
neuromuscular junction: N-CAMs
are part of what hold the presynaptic
plasma membrane in position across
from the motor endplate of the post
synaptic plasma membrane.
Cadherins are a class of Ca++Dependent cell-cell adhesion molecules
which are important in embryogenesis. Their loss permits cells to migrate
within the chick embryo to become muscle.
Dimer anchored by tx-membrane sequences
Localization of sub-types:
E-epithelial N-neuronal P-placental VE-endothelial
For instance: N-cadherin binds to other N-cadherins, but not
to E, P or VE-cadherins
This keeps neurons attached to other neurons!
Important to vertebrates and invertebrate animals
Classic exrracellular Cadherin binds to actin on intracellular side.
Non-Classic binds tonofilament on inside: for extra strength
If potential neurons don’t lose N-cadherins, they can’t migrate!
About 85% of cancers are epithelial in nature (due to high
replication rate), metastasis is linked to a loss of E-cadherins
Integrins: transmembrane proteins with an extracellular ICAM binding domains.
White blood cells tend to “Roll” along the surface of blood vessels looking for trouble
(a signal of damage outside vessel). When damage occurs endothelial cells move
P-selectin from vesicle to the cell surface and this binds the leukocyte glycoproteins!
Then integrin binds its ICAM!
What amino acids would you expect at the locations where the glycosylations occur on
glycophorin? Why is the carbohydrate sialic acid (-charged) important for the
extracellular side on an RBC? When the erythrocyte has circulated for about 60-120
days, the sialic acids and glycosylations will have rubbed off to expose the receptor,
which mediate lysis in the spleen or liver. ]
Extracellular glycoproteins can mediate cell-cell interactions too!
How does the body know when to destroy a red blood cell that is 120
days old or older? Solution: selective removal of RBC sialic acids.
What does sialic acid,also called N-acetylneuraminic acid (NANA), look like?
What is it’s net charge?
NANA attached to glycoprotein
No NANA: N-CAM Exposed!
Cell binds to macrophage
Removal at spleen/liver
120 day life-span
1 trillion RBCs in the body
1 pint/30-60 days!
Neuraminase removes NANA
1 million cells removed/second
Fibronectin is an important mediator between cells and
the contents of the matrix.
Generally found as a extracellular dimer crosslinked by a pair of
dissulfides (-S-S-)
• Each subunit (dimer) contains different domains, each domain has a
potentially different function.
• Sample domains:
– Fibrin binding Form clot
– Heparin binding Clot lysis
– Collagen binding bind where tissues exposed
– Cell surface receptorshold cells down, this is why tissue culture
plates are typically coated with a thin layer of collagen or
fibronectin!
– Collagenase is used when you want to remove cells from a culture
dish.
There are several discrete structures that are observed at the locations
where the adherence molecules bind cells together.
Two other cell surface receptors:
Basal Lamina: found underneath all epithelial cells in the body and creates a matrix
for cellular attachment/protection
• Laminin protein: primary constituent
–
–
–
–
Large peptide (alpha, beta, gamma subunits)
Dense packing
Cross-shape
Many potential binding domains
• Integrin: helps create a link to intracellular proteins
–
–
–
–
–
Large dimer (alpha and beta subunits)
Extracellular aspect- binds matrix or ICAMs
Intracellular aspect- indirectly binds actin (via tallin and vinculin)
Also an integral part of hemidesmosome
Extracellular binding is often linked to changes in activity of protein kinases
in the cytosol
Cell-Cell adhesions can occur at specifics locations.
What are some of the classic locations?
• Desmosome: button of contact specialized for stress!
– Dense deposit of tonofiliments!
– Narrow intercellular space!
• Hemidesmosome: attachment to lamina
– Contains tonofilaments,,, sort of ½ of a desmosome!
• Adherence Junctions: Belt-like or Focal
– Bands of attachement
– Continuity with actin in muscle actin/myosin complex
• Tight Junction: Protein belt for molecular
impermeability
– Important where body meets external environment: gut,
skin, kidney
• Gap Junction: connexins to allow small molecule
diffusion between cells.
– Especially important in the heart!
Often times bacteria and viral particles have special receptors that fill the
receptors on the cell, causing the host to pull cell inside!
•
Once inside pathogen can
disable cell!
•
Disabled cell is “hijacked” by the
pathogen and protected by the
cell!
•
Examples: HIV-Virus, Anthrax,
Listeria, Shigella and Yersinia
•
Most Effective Targets: Immune
Cells!
•
•
Common Receptor Targets:
Integrin and E-cadherin
Tight Junctions are critical for maintaining water impermeability at places
where cells meet the external environment!
• Why are TJ critical in the gut, kidney and skin?
– Where would the water go?
• There is no measurable space between adjacent cells bound by
TJ!
• TJ Blocks:
• 1) ….movement of ions, water and proteins between these
adjacent cell
• 2) ….Movement of proteins between the outside (apical) and
inside (basolateral) aspects of the plasma membrane.
• TJ consists of a mesh-like band of thin proteins that wrap entirely
around cells many many times. The proteins (claudins and
occludin) of the two cells bond to each other pulling the two cells
very tightly together forming an impermeable barrier.
The claudin and occludin subunits of the two adjacent cells form a belt
around the lateral aspect of the cell, typically on the apical side.
Tight Junctions mean that the only way materials can enter a cell is
to pass through the transport enzymes of the apical membrane, pass
though the cytoplasm, and use a different enzyme on the basolateral membrane. (2 Diff. Tx Enzymes)
This gives a precise way for a cell to regulate transport!
Gap Junctions are specialized pores consisting of two connexons that link
the intracellular contents of adjacent cells.
This arrangement allows small molecules to physically pass between cell
and is especially important in the heart!
• Pores are critical for permitting
the movement of ions during AP
propagation between heart cells!
• Pores create a functional
“syncitium” in the heart!
• Connexons may also be
important for the passage of
water, sugars and amino acids.