Dr. Missiakas’s research program examines the Gram-positive pathogens Staphylococcus aureus and Bacillus anthracis. This program seeks to appreciate the biogenesis of the envelope of these microorganisms as well as the secretion of their virulence factors and host pathways targeted by these pathogens.
Pathogenesis and vaccine studies in S. aureus:
Many molecules in the envelope of these bacteria affect their interactions with the host. In staphylococci, cell wall anchored proteins contribute to pathogen survival in blood, dissemination to tissues, formation of abscesses and persistence in host tissues as well as subversion of immune functions. The systematic analysis of mutants lacking all or anyone of twenty cell wall anchored proteins has proven a very powerful approach in identifying protective antigens for vaccine design and elucidating virulence pathways.
S. aureus is the only bacterial pathogen known to coagulate plasma and to agglutinate with fibrin cables in blood. A molecular examination of agglutination revealed that this process requires the secreted products of the coa (coagulase), vwb (von Willebrand binding protein), and clfA (Clumping factor A) genes. We are examining a model whereby S. aureus agglutination involves the formation of staphylothrombin (Coa, vWbp)-assembled fibrin cables, capped by clumping factor A (ClfA) on the staphylococcal surface and crosslinked by factor XIII. In this model, S. aureus agglutination provides for escape from phagocytic killing and bacterial traffic across the vasculature. In this manner, the Coa-vWbp-ClfA mediated agglutination pathway promotes the formation of abscess lesions, where S. aureus replicates as a fibrin encapsulated bacterial community, protected from immune cells. This key virulence strategy can be perturbed with monoclonal antibodies and small molecule inhibitors to either prevent or treat S. aureus sepsis
Cell envelope assembly:
Bacteria assemble polymers in their envelope that are important for their viability as well as their interaction with hosts. Our research program combines bacterial genetics, physiology and biochemistry as well as small molecule chemical tools approaches to characterize the complex biochemical pathways that enable envelope assembly in Gram-positive microbes. Potential innovations derived from this work are the identification of key enzymes for the biosynthesis of lipoteichoic acid (LTA), wall teichoic acid (WTA), secondary cell wall polysaccharide (SCWP) and capsular polymer (CPS, PDGA). In Bacilli, the SCWP is also involved in the retention of proteins that bear the S-layer homology domain (SLH proteins). SLH proteins play important function for cell separation, sporulation as well as virulence.
One aspect of this program examines a Sec-independent secretion system named ESAT-6 like Secretion System (ESS). Biochemical and genetic approaches are used to isolate and characterize the ESS translocon, identify secreted substrates and elucidate their function during infection of hosts.