From: ncbi-seminar-admin@ncbi.nlm.nih.gov on behalf of Michael Galperin
[galperin@ncbi.nlm.nih.gov]
Sent: Thursday, February 27, 2003 3:12 PM
To: ncbi-seminar@ncbi.nlm.nih.gov
Subject: CBB seminar March 4th

Pushing the (cell) envelope: Studies of surface-exposed bacterial proteins

Michael Galperin

Tuesday, March 4th, 11:00 am, Bldg. 38A, 5th floor conference room,

Surface-exposed (extracytoplasmic) proteins participate in the 
interaction of bacteria with the environment and define their specific 
antigenic properties. As a result, such proteins typically exhibit 
higher diversity then the cytoplasmic proteins and do not necessarily 
fit into the existing protein families (COGs, CDDs).  Nevertheless, 
rapid growth of the list of completely sequenced bacterial genomes 
brings into the database homologs of many extracytoplasmic proteins and 
allows their comparative analysis.

Our studies of surface-exposed proteins centered on three groups of 
proteins: (i) proteins involved in the Na+ cycle (generation and 
maintenance of the sodium-motive force); (ii) signal transduction 
proteins with periplasmic or integral membrane sensory domains; (iii) 
surface-anchored proteins of Streptococcus pneumoniae.  I will describe 
several interesting domains, delineated in the course of these studies, 
and discuss the following ideas brought about by this analysis:
(i) The choice between Na+- and H+-dependent energetics seems to depend 
on the aerobic/anaerobic lifestyle of the organism, rather than on it 
being a bacterium or an archaeon, its growth temperature or pathogenicity.
(ii) Association of certain conserved sensory domains with various 
signal output domains allows microorganisms to sense the environmental 
signals (e.g., pH, osmolarity) and transmit this information to 
different regulatory circuits: transcriptional regulation, chemotaxis, 
catabolite repression, and production of extracellular factors.
(iii) The pneumococcal cell envelope contains a number of surface 
proteins with various enzymatic activities, some of which (but not all) 
can be interesting vaccine candidates.