Scheduled Seminars on 10/2/2012

Dapeng Zhang at 11:00  Edit  Reschedule  Delete

Dissecting polymorphic toxin systems by domain analysis and comparative genomics
The availability of an enormous wealth of genomic sequence data has provided unique opportunities for biologists to understand function and mechanisms of diverse biological pathways. Here by using a domain-centric strategy with comparative sequence, structure and genome analysis, we have identified a novel and widespread system of bacterial toxins in all major bacteria lineages. The toxins in this system are featured by three functional modules, N-terminal secretion related domains, central domains that may contain RHS and haemagglutinin repeats, pre-toxin peptidases, which are predicted to release the toxin, and C-terminal toxin domains. To date, we have identified and characterized over 150 distinct toxin domains that display diverse biochemical activities such as nuclease, deaminase, peptidase, kinase, ADP-ribosyltransferases and pore-formation. Additionally we report three primary toxin-releasing peptidases of the metallopeptidase, caspase and HINT superfamilies, and many N-terminal domains that mediate at least seven different secretion pathways for facilitating toxin translocation. An examination of the genome neighborhoods, revealed over 90 families of immunity proteins that are predicted to block the activities of the self and non-self toxins. Two of the primary types of immunity proteins include members of the SUKH and SuFu superfamilies. The interaction of polymorphic toxins and immunity proteins appears to play a major role in inter- and intra- specific conflicts in bacteria. In this presentation, we will discuss the primary components of the toxin domains and immunity proteins, secretion pathways for toxins, genomic organization, as well as the evolutionarily diversification mechanisms. We will also discuss several prominent instances of lateral transfer of the toxin system to eukaryotes and their viruses.

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