Yale Bulletin and Calendar

September 27-October 4, 1999

Volume 28, Number 6

Scientists unravel 'yin' and 'yang' of how
salmonella uses proteins to spark disease

In order to promote favorable living conditions once it invades a cell, the salmonella bacteria injects its host cell with a protein called SptP, a Yale study finds.

"These findings bring us closer to understanding the complex mechanisms by which these bacteria cause disease and may lead to development of new therapeutic and prevention strategies," says Jorge E. Galan, professor in the section of microbial pathogenesis at the School of Medicine.

Salmonella is a pathogen, or disease-causing bacteria, that brings about a variety of illnesses ranging from common food poisoning to the more severe, even life-threatening typhoid fever.

To gain access and cause disease in the body's cells, salmonella injects a bacterial protein called SopE into the cell. The protein coaxes the cell into taking it inside by "tripping" molecular switches in the cell. SopE then stimulates the cellular responses salmonella needs to gain access. However, the same cellular responses that allow the bacteria to enter the cell will also kill the host cell. To prevent this, Galan says, salmonella injects a second protein called SptP into the cell.

"This second protein has the ability to actually 'turn off' the molecular switches called CDC42 and Rac that are activated by the function of the SopE protein," explains Galan. "The 'yin' and 'yang' relationship between these two bacterial proteins constitute a remarkable example of the sophisticated strategies salmonella uses to suppress normal host cell functions for its own advantage."

Gaining access to the inside of the host cell gives salmonella an opportunity to replicate, to avoid host defense mechanisms, or to reach deeper tissues. Galan's study helps advance scientists' understanding of how salmonella manipulates host cell function.

In his research, Galan also found that pathogens like salmonella that have co-evolved with their hosts for millions of years have "learned" intimate details of host cell functions which could be extremely useful in teaching basic important aspects of cell physiology.

Galan performed the study with the help of Yixin Fu, who was a graduate student at Yale's Boyer Center for Molecular Medicine.

-- By Karen Peart

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Former V.P. of European Commission named visiting scholar at Yale SOM

Philanthropist and builder Frederick P. Rose '44E dies

Astronomers say universe expanding faster than once thought

Scientists unravel 'yin' and 'yang' of how salmonella uses proteins to spark disease

Chemist to study potential benefits of sea sponge molecule with $150,000 grant

First winners of Frederick Douglass Book Prize named

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Employee Day at the Yale Bowl

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