101
The Science of
Connexin
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What you will learn in Connexin 101?
¤ Transition of single-cell life to
multicellular life.
¤ What is a connexin molecule?
¤ How connexins allow cells to
communicate.
¤ Why the whole is greater than
the sum of its parts.
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Single Cell to Multi-cellular Life
¤ Single cell life is believed to have
existed on Earth for 2-3 billion years.
¤ Approximately 600 million years
ago the connexin molecule
mysteriously appeared on Earth.
¤ At that time, multi-cellular organisms began
appearing as well. The ultimate multicellular
organism to date is man, homo sapien.
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So what is a Connexin?
6 connexin protein subunits
¤ A connexin is a molecule composed of 6 protein subunits.
These proteins join to form a structure which has a opening at
its center.
¤ Currently, 21 types of protein subunits can be combined to form
many different connexin molecules each having unique
molecular properties.
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So what is a Connexin?
¤ Imagine these 6 subunits coming together. An opening, hole,
or pore is formed in the middle of these radially joined proteins.
¤ These 6 subunits (proteins) form a unit known as a connexon
which lies in one cell’s membrane.
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So what is a Connexin?
In this cutaway diagram, notice that when two open connexons are
joined, the opening or pore can allow continuous flow of materials.
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So what is a Connexin?
Pore
Central Opening
Cell
membrane
When 6 connexin protein subunits come together in a
cell’s membrane they form a unit with a central opening
or pore called a connexon.
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So what is a Connexin?
Cell membrane
Cell membrane
Two connexons, one in each cell’s membrane, dock together to
form a channel of communication between two cells.
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So what is a Connexin?
The above shows the total process of connexin formation.
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The Connexin Pore
Closed Pore
¤This is a depiction of a closed connexin pore.
¤Note that only the smallest molecules, if any at all, can
pass through this small central opening.
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The Connexin Pore
Open Pore
¤ This in comparison is a rendition of an open
connexin pore.
¤ The size of the pore allows for many molecules to
pass through its central opening.
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The Connexin Pore
Open Pore
Closed Pore
¤ The figure on the left represents an open connexin
molecule.
¤ The figure on the right shows the same connexin
molecule exposed to cellular conditions that close
or reduce the opening.
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Connexins in a Membrane
Small molecule
Large protein
Cell membrane # 1
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This diagram shows 3
connexons in a cellular
membrane. Notice that
small molecules (the small
round spheres) can pass
through the opening,
whereas the large folded
proteins cannot.
A Cell With Many Connexins
Cell #1
Cell membrane
Connexon
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Connexins in a Membrane
Small molecules
This rendition also shows
3 connexons in a cellular
membrane. Again, notice
that small molecules (the
small round spheres) can
pass through the opening,
whereas the large folded
protein cannot.
Large protein
Cell membrane # 2
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Another Cell With Many Connexins
Cell # 2
Connexon
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The Connexin Pore
Cell # 1
Cell # 2
¤ Molecules can be exchanged by
cells if they are small enough to
pass through the connexin pore.
¤ This size restriction is influenced
by the diameter of the opening or
pore.
¤ The size of this opening is under
the influence of both molecular
and physical conditions in a cell
at a given point in time.
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Two Cells Joined by Connexins
Cell # 1
¤ As we discussed, a pore or
channel is formed in a cell’s
membrane by the 6 protein
subunits which make up a
connexon. This pore or opening is
not static, but its diameter is
influenced by both its molecular
structure and also by physical and
molecular factors in our body.
¤ The connexin pore or opening
allows for molecular and electrical
continuity and exchange between
cells.
Cell # 2
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Multicellular Life
¤ Connexins are involved in the
regulation of our cells.
¤ By integrating our cells,
connexins make multicellular
life possible.
¤ Our cells now communicate
with one another and are able
to work together.
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Connexin Number
¤ Cellular communication is enhanced when the connexin
molecules’ pore is open.
¤ More open connexin molecules present on a given cell when
joined to other cells, leads to greater cellular communication.
¤ The number of connexin molecules present on a cell is
influenced by the types of molecules to which a given cell is
exposed as well as environmental conditions.
Example: Pregnancy induces more connexin molecules to sit on
the surface of uterine muscle cells. This leads to contractions at
the end of a women’s term pregnancy.
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Connexin Number
¤ Injury and repair of tissues involve expression of
different connexin molecules and a change in
connexin molecule number.
¤ When tissues are disrupted, the degree of injury
needs to be communicated to surrounding cells.
¤ Then new molecules and cells need to be formed
and sent to the region of injury to repair the damage.
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Trillions of Connexins Join Trillions of Cells
¤ A good way to think about cellular connectivity is depicted by
Dali’s 1952 painting, Galatea of the Spheres.
¤ A recognizable woman is visualized from a collection of
spheres. We are like a collection of spheres – cells!
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Trillions of Connexins Join Trillions of Cells
Courtesy: www.TeamSandastic.com
Now imagine a sandman made up of millions of tiny sand particles
(spheres), each sand grain larger than one of our living cells. But our
cells are connected and function as a unit such that the whole is greater
than the sum of its parts.
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What have we learned in Connexin 101?
¤ How single-cell life transitioned
to multicellular life.
¤ All about the connexin
molecule.
¤ How connexins enable
cell-to-cell communication.
¤ Why the whole is greater than
the sum of its parts.
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Congratulations!
You have completed course 101!
We hope you continue your Molecular Fitness
education by participating in more ConnexinCollege
courses.