Caltech biologists spy on the secret inner life...(eries of static images by taking them at...)

Date:10/12/2008

eries of static images by taking them at different time points," says Bjorkman, whose laboratory studies how the immune system recognizes its targets, work that is offering insight into the processes by which viruses like HIV and human cytomegalovirus invade cells and cause disease.

The electron tomography images revealed that the FcRn/antibody complexes were collected within cells inside large vesicles, called "multivesicular bodies," that contain other small vesicles. The vesicles previously were believed to be responsible only for the disposal of cellular refuse and were not thought to be involved in the transport of vital proteins.

The images offered more surprises. Many vesicles, including multivesicular bodies and other more tubular vesicles, looped around each other into an unexpected "tangled mess," often forming long tubes that then broke off into the small vesicles that carry antibodies through the cell. When those vesicles arrived at the blood-vessel side of the cell, they fused with the cell membrane and delivered the antibody cargo. The vesicles also appeared to include a coat made from a molecule called clathrin, which helps form the outer shell of the vesicles. Researchers previously believed that a vesicle's clathrin cage was completely shed before the vesicle fused with the cell membrane. The new results suggest that only a small section of that coating is sloughed off, which may allow the vesicle to more quickly drop its load and move on for another.

"We are now studying the same receptor in different types of cells in order to see if our findings can be generalized, and are complementing these studies with fluorescent imaging in live cells," Bjorkman says. "The process of receptor-mediated transport is fundamental to many biological processes, including detection of developmental decisions made in response to the binding of hormones and other proteins, uptake of drugs, signaling in the immune and nervous systems, and mor
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Contact: Kathy Svitil ksvitil@caltech.edu 626-395-8022 California Institute of Technology Source:Eurekalert

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