The Wright Lab

Obscurin

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The cell is held together through a web-like mesh of proteins called the cytoskeleton.  This is more than just a scaffold.  Of course the cytoplasm has to be strong- cells must withstand a variety of different stresses and strains without rupturing. But cells also must be able to move, so this scaffold also has to occasionally be very pliant.  Additionally, cells must be able to recognize when they should move and when they should be strong.  So the cytoplasm also has to sense, interpret, and then respond to external signals.

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One way cells can do this is through giant cytoskeletal proteins- proteins like titin and obscurin.  These proteins resemble a long chain, and serve to connect different pieces of the cell to one another.  For instance, titin connects bands of muscle together.  If the muscle gets stretched too much, titin acts as a molecular spring, preventing further overstretching!

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Obscurin looks very similar to titin, but isn't in the right orientation to act like a spring in the same way; often, it seems to be wrapping around the muscle.  What, then, is it doing?  Our lab has shown that it is linked to motility, at the very least; there are at least 4 independent mechanisms of how obscurin stops cells from moving.

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When you knock out obscurin, cells move faster.  When you add obscurin back in to cells, they move slower.  How is obscurin regulating this on a molecular level?  Likewise, what is controlling obscurin?  

 

 

 

 

 

 

 

 

 

 

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To study all these questions, we use a braod set of techniqued.  We use heteronuclear multidimensional NMR to see, in atomic resolution, what the protein and various mutants look like and how they move.

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We also use molecular dynamics simulation to explore how obscurin acts when pushed or pulled, or what happens to the domains when they are mutated. 

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Last, use use cell culture techniques to explore how obscurin acts in the context of the whole cell.  We use live-cell imaging, FLiM, and interaction methods like BioID to figure out where obscurin is located, what it is binding to, and what kinds of stress obscurin (and the cell) are under in various conditions.  Our hope is that these studies can better explain how cells respond to their environment.

 

Long term, these studies this might lead to better treatments of human diseases.  In fact, this process is already underway- our lab has successfully explained the molecular mechanism of how a variety of cardiomyopathies and muscular dystrophies arise.  Our more recent work showing how obscurin is linked to motility has implications in explaining how cancer cells stop listening to their environmental cues telling them to stop moving and/or dividing.   Our insights will, with time, lead to the development and construction of more intelligent remedies!

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Desmoplakin

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If the cytoplasm hold the inside of cells in place, proteins like desmoplakin allow cells to hold on to each other.  Desmoplakin is part of the desmosome, which acts like glue to muscle and skin cells.  If the desmosome is gone or deficient, muscle cells (and skin cells) don't attach to each other correctly.  This leads to cells tearing away from each other, and eventually leads to some nasty diseases including arrhythmogenic cardiomyopathy. This is the disease where your heart just suddenly stops beating.

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It turns out that lots of desmoplakin mutations are linked to arrhythmogenic cardiomyopahy.  We recently showed that for some mutations, this is due to desmoplakin mutants being hypersensitive to calpain.  This protease degrades desmoplakin, weakening cell-cell junctions. In collaboration with Maegen Borzok's lab at Commonwealth U., we have shown that we can counteract this by physically blocking the calpain cleavage site.  This can be done specifically by targetting desmoplakin, without interfering with normal calpain functions.  This exciting project has potential to offer treatments for Arrythmogenic Cardiomyopathies.are now working on how we might be able to use this newly-found molecular mechanistic information to specifically prevent desmoplakin degradation, without interfering with other noramlly-occuring calpain functions.

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