QUOTE: "...Based on accepted theories, we expected crowding to affect proteins in the unfolded state," said Rice biochemist Pernilla Wittung-Stafshede, one of the study's co-authors. "We were surprised when both experimental evidence and computer simulations showed that crowding also acts directly upon proteins in the folded state."
Living cells are crowded places. They're filled with a chemical soup of 100-300 mg per mL of large molecules, such as DNA, proteins and ribosomes. This corresponds to about 40 percent of volume occupancy.
"The consistency is very viscous," said Wittung-Stafshede. "It's something like Jell-O or the freeway at rush hour..."
Using sucrose-based polymers (inert synthetic mimics of real macromolecules), the pair created several test environments designed to mimic the gooey milieu that proteins experience inside a cell. Using spectroscopic methods, Stagg and Wittung-Stafshede then probed how the structural content as well as the thermal stability of apoflavodoxin changed as a function of added crowding agents...
The researchers found the protein's native state becomes more compact and more ordered. The secondary structure of the folded protein increased by as much as 25 percent based on circular dichroism data...
Proteins are the workhorses of biology, and their form and function are intertwined. Proteins are chains of amino acids strung end-to-end like beads on a necklace. The order comes from DNA blueprints, but proteins fold into a 3-D shape as soon as the chain is complete, and scientists can determine a protein's function only by studying its folded shape. It is still an open question how a long floppy chain of amino acids is programmed to adopt a unique 3-D shape in a timely manner (often seconds to minutes)... UNQUOTE.
Source: http://www.sciencedaily.com/releases/2007/11/071112172136.htm |
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