Other projects

We are pursuing several other projects:

Protein-protein interactions

We are studying stable protein complexes involved in a variety of biological functions. Here are examples of two complexes involved  in the assembly of Fe-S clusters.

IscS-IscU-TusA

Lenght regulation of cell surface polysaccharides

Bacterial surface polysaccharides provide a protective layer and are essential virulence factors present on the surface of major bacterial pathogens. Although the genes involved in the complex process of their synthesis and export to the cell surface have been identified, the mechanistic details are largely unknown. The early steps in the biosynthesis of Wzy-dependent repeat unit polysaccharides have a common underlying mechanism in that it occurs on either side of the inner membrane, involves undecaprenol (bactoprenol)-linked intermediates, glycosyl transferases that assemble the repeat unit (3 to 5 sugars) in a sugar and glycosidic linkage-dependent manner, a transporter (termed Wzx) that translocates the repeat unit from the cytoplasmic to the periplasmic side of the inner membrane, and a polymerase (termed Wzy) that joins together the repeat units by successive transfer of the growing undecaprenol linked sugar repeat chain to the reducing end of a single repeat unit. This synthesis has also been termed the Wzy-dependent pathway. Subsequent steps in biosynthesis and export vary depending on the nature of the final product (lipopolysaccharide (LPS), capsular polysaccharide (CPS), extra-cellular polysaccharide (EPS), Enterobacterial Common Antigen (ECA), teichoic acid (TA), lipotechoic acid (LTA), and whether the bacteria are Gram-negative or Gram-positive. This process has similarities to the glycosylation of proteins in the ER of a eukaryotic cell in that the oligosaccharide repeat unit or core is synthesized in the cytoplasm on a lipid carrier anchored in the ER membrane, flipped by a flippase across the membrane and the chain finally transferred to an acceptor protein.

Polysaccharide Co-Polymerases (PCPs) play an essential role in determining the length distribution of the synthesized polysaccharide chain. Bacterial PCPs, a family of over 1150 proteins, participate in the biosynthesis of cell-surface polysaccharides and have been grouped into three classes. Common features of all PCPs are the presence of N-terminal and C-terminal transmembrane helices (TM1 and TM2) separated by a ~130-400 residue polypeptide segment having a predicted coiled-coil region located in the periplasm (or externally) and a Pro/Gly-rich sequence motif adjacent to and overlapping with TM2. The sequence similarity between the three PCP classes is very low and can be low even within each class. Wzz proteins, the most thoroughly studied PCPs, belong to the PCP1 group and have a ~240-280 aa (36 to 40 kDa) hydrophilic, periplasmic region. The ability of Wzz proteins to control Oag chain length is crucial for bacterial virulence and invasion of host cells.

PCPs