The main area of my expertise concerns protein sorting and secretion in Gram-positive bacteria, such as Bacillus subtilis and Staphylococcus aureus.
The Gram-positive bacterium B. subtilis is well known for its high capacity to secrete proteins into the extracellular milieu, which has led to its exploitation as a "cell factory" for secreted proteins. Nevertheless, the secretion of heterologous proteins of pharmaceutical importance is frequently inefficient. This applied problem has been a major incentive for fundamental research on the mechanisms of protein transport in B. subtilis. For this purpose, molecular biological, phylogenetic, genomic and proteomic techniques were employed in an integrated way to study the mechanisms of protein secretion in B. subtilis. More recently Systems Biological approaches were implemented for the research on protein secretion, including so-called live cell array technology. Important research outcomes were: (i) characterisation of a Gram-positive Tat pathway for protein transport; (ii) novel insights in the roles of lipid-modification in membrane-attachment and function of lipoproteins of Gram-positive bacteria; (iii) a strategy for improved disulphide bond formation in secreted proteins; (iv) description of the B. subtilis response to protein overproduction and secretion stress; and (v) bioinformatic and proteomic descriptions of the B. subtilis secretome. Ongoing research is focused on the dynamic behaviour of the secretome in response to changing environmental conditions.
Staphylococcus aureus is an important hospital- and community-acquired opportunistic pathogen. Recent research on protein sorting and secretion in S. aureus has yielded a state-of-the-art roadmap of the S. aureus secretome. The secretome map includes both protein transport pathways and the extracytoplasmic proteins. This has resulted in overviews of the exported virulence factors, pathways for protein transport, signals for cellular protein retention or secretion, and the exoproteomes of clinical S. aureus isolates. Importantly, the results include a first definition of the core and variant secretomes of S. aureus. While the core secretome seems to be largely employed for general house-keeping functions, necessary to thrive in particular niches provided by the human host, the variant secretome seems to contain the "gadgets" that S. aureus needs to conquer these well-protected niches (Sibbald et al., 2006). Ongoing research is aimed at analysing how the different secretion pathways of S. aureus impact on exoproteome biogenesis, fitness, resistance to antibiotics, adhesion to biomaterials and cell components, biofilm formation and virulence.