Alfonso Felipe-López


C1 The structural and functional basis of reprogramming of vesicular transport by Salmonella enterica effector proteins

Principal investigator
Michael Hensel

Andreas Burkovski

Molecular analysis of the large non-fimbrial adhesins in S. enterica sv. Typhimurium

Salmonella enterica sv. Typhimurium (S. sv. Typhimurium) is an important human pathogen of the intestinal tract. Successful invasion and disease development appear when bacteria have adhered at the mucosal membrane of the intestine. Therefore, we are interested to study the function and expression of the large non-fimbrial adhesin encoded in the genome of S. sv. Typhimurium. As part of this project, we want to address the question how STM3691 (Salmonella adhesin A-SadA) is regulated and what is its function. Luciferase-reporter strains revealed that STM3690-sadA expression is controlled by a putative promoter sequence upstream of STM3690-sadA. Since the expression of STM3690-sadA was3-5 times lower in LB- or PCN-glucose medium compared to PCN-mannitol medium, it seems likely, that the carbon source influences the expression, too. Upstream of STM3690-sadA is the mannitol-phosphotransferase system (Mannitol-PTS) operon encoded. This operon is under control of a repressor (MtlR) which interacts with DNA-binding protein FIS. Mannitol modifies allosterically the MtlR structure so that neither any interaction with DNA and FIS nor constraining of DNA occurs. Probably, the lost of interaction between FIS-MtlR allow the expression of STM3690-sadA.
In order to investigate the role of SadA in invasion on different polarised cells sadA-overexpressing strains were constructed which were either under control of SPI4 or invF in a SPI4 deficient mutant. Unfortunately, invasion experiments with CaCo2bbe1, T84 and MDCK cells showed that these strains were unable to recover the invasion provided by SPI4. Independent experiments revealed that invasion was reduced in an sadA-mutant strain. Altogether, these results suggest that during infection, structural modifications of the sadA promoter must occur either due to the presence of mannitol or by molecules which are able to modify the DNA structure that as a result the expression of sadA is induced. However, these modifications should appear when the endosome is being formed, but not before the Type III Secretion System I is expressed.
Further studies should reveal whether transcription factors are responsible for expression of sadA in order to predict at which stage of the infection SadA is required. Additionally, it will be analysed if SadA has actually a general function in the invasion process in mammals cells and whether it is also useful for invasion in other organisms like plants.

Figure: SadA (green) overexpressing strain MvP 1336 of Salmonella enterica sv. Typhimurium (red) adheres on the lateral cell membrane of the CaCo2bbe1 cells after 7 days of incubation (nuclei-pink), promoting actin movilization (blue) at the site of bacterial adhesion.



Felipe-López, A., Pérez-Nieves, I., Gómez-de-León, P., Rocha-Gracia, R., Díaz-García, J. and Giono-Cerezo, S. (2007). Beta-lactamases TEM1 and genomic island ICEHin1056 in Haemophilus influenzae Mexican strains. (in preparation)



September 2010 2nd Annual Retreat, Erlangen School of Molecular Communication, Kloster Banz, Bad Staffelstein, Germany
Cooperation Between Two Secretion Systems in Salmonella sv. Typhimurium”
September 2009 First Annual Retreat, Erlangen School of Molecular Communication, Schloss Atzelsberg, Atzelsberg, Germany
Expression and function of STM3691 (Salmonella Adhesin-A)”
October 2007 11th International Congress on Culture Collections. Goslar, Germany
Haemophilus influenzae ATCC 33930 as a model for resistant and virulence traits.”
June 2006 12th International Congress on Infectious Diseases, International Society for Infectious Diseases. Lisbon, Portugal
“Beta-Lactamases TEM1 by PCR in Haemophilus influenzae Strains from Mexican Patients.”