Bacterial Membranes - CNRS URA2172  

CWERMAN Hélène / Dr DASSA Elie / Dr DELEPELAIRE Philippe / Dr LETOFFE Sylvie / Dr NUNEZ SAMUDIO Virginia

  Annual Report


The increasing number of available genome sequences brings mountains of data that are not easy to interpret. Even in bacteria, half of the genes encoding polypeptides have unknown functions. Moreover, several polypeptides have more than one function.

Bacterial genetics is a powerful approach to discover new functions. Our laboratory has identified several new bacterial functions including those of TolC, hemophores, dipeptide permease etc. Most of these achievements were start points of biochemical and biophysical studies performed with various collaborators.

Heme acquisition across the outer membrane

Heme is the prosthetic group of many proteins, and is also a major iron source (an essential metal). Several bacteria such as Serratia marcescens have heme acquisition systems depending on secreted hemophores (HasA). HasA scavenges heme from various hemoproteins due to its higher affinity for this compound, and returns it to its specific outer membrane receptor HasR which has a lower affinity for heme and binds also heme-free and heme-loaded hemophores. Heme transfer from the hemophore to the receptor is energy independent and driven by the HasA-HasR protein-protein interactions (J.Biol.Chem.2006). In contrast, heme transport and empty hemophore recycling require energy. In addition, heme loaded HasA binding to HasR triggers the Has system induction, allowing adaptation to the available iron source. (J. Bacteriol. 2006)

Heme transport through the inner membrane

The specific E. coli heme permease is constituted by the dipeptide ABC importer and two optional periplasmic peptide binding proteins which both bind heme (Proc.Natl.Acad.Sci. 2006). Our results invalidate the hypothesis of non specific partitioning of heme through the inner membrane. We are actually testing whether generally, heme and peptides share common transporters. This might have implications for the design of new heme-permease inhibitors.

Protein secretion

Many proteins including hemophores are secreted by a transporter comprising one ABC protein and two helper envelope proteins. The secretion signal usually located at the C-terminus interacts with the ABC protein, modulates its ATPase activity and induces the formation of a secretion multiprotein complex. A hemophore mutant lacking its secretion signal is not secreted, but still interacts with the ABC protein and promotes a stable complex (J. Bacteriol.2007). We are studying the dynamics of the complex dissociation induced by the secretion signal.

ABC proteins lacking transmembrane domains

Uup is an ABC protein of unknown function. The deletion of the gene encoding Uup leads to an increase in precise excision of transposons. Analysis of Walker motif B mutants suggests that ATP hydrolysis at the two ABC domains is essential for the function of Uup in vivo.

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Publications 2006 of the unit on Pasteur's references database

Activity Reports 2006 - Institut Pasteur
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