Areas of Interest
Molecular assembly on the cell surface of Gram-positive
bacteria, bacterial pathogenesis and host-pathogen interactions.
Pilus assembly
Pili have been identified in many Gram-positive pathogens,
however, the mechanism of pilus assembly and function of pili
are just beginning to be unraveled. Best understood is the
mechanism of the prototype SpaA pili found in Corynebacterium
diphtheriae, the causative agent of diphtheria that
assembles three distinct pilus structures, designated as SpaA-type,
SpaD-type and SpaH-type pili (Spa for sortase-mediated pilus
assembly). Similar to other types, the SpaA-type pili are
composed of three pilin subunits, SpaA, SpaB and SpaC. SpaA, the
major pilin, forms the pilus structure, while SpaB is
incorporated along the pilus shaft and SpaC largely positioned
at the tip. The assembly of SpaABC pili requires sortase SrtA
located within the pilus gene cluster. According to the current
model, pilus precursor proteins containing the N-terminal
secretion signal are synthesized in the cytoplasm and
transported across the cytoplasmic membrane by the general
secretion (Sec) machinery. Upon translocation to the exoplasm,
the pilus precursor proteins are captured by a specific sortase
and assembled into high molecular weight structures which are
subsequently anchored on the bacterial cell wall. Interestingly,
our recent work revealed that the minor pilins SpaB and SpaC are
not only part of the pilus structures, but they are also
anchored in close clusters on the cell wall. These observations
open up several intriguing mechanistic and biological problems.
How are pilins assembled? Is pilus assembly compartmentalized?
Are there factors that regulate pilus polymerization and the
surface display of pilins? Does this regulation involve cues
from the host? Our current work is devoted to answering these
fundamental questions using C. diphtheriae as a model.
Universality of pilus assembly in Gram-positive bacteria
Our prediction that sortase-mediated pilus
assembly is universal in Gram-positive bacteria is supported by
recent work by several research groups. Consequently, our
laboratory is now investigating the assembly and function of
pili in Actinomyces spp., early colonizers of human
teeth, and in group B streptococcus, which is the leading cause
of bacterial pneumonia, sepsis and meningitis among neonates.
Efforts are made to find the common features of pilus assembly
and the role of pili in pathogenesis.
Pili in pathogenesis
Available evidence indicates that Gram-positive pili are
involved in host-tissue adhesion, co-aggregation and immuno-modulation.
Importantly, Gram-positive pili have been explored as vaccine
candidates. We are employing ex-vivo tissue cultures, infection
of worms and rodent models to address several aspects of
bacterial pathogenesis: Are pili required for bacterial
infection? How are pili involved in tissue tropism? How do pili
modulate the host immune system?
Lab Rotation Projects
The projects will be designed centering on the three major
problems above and individual student interests. Basic approach
to these studies is a combination of immuno-fluorescence and
electron microscopy, mass spectrometry, biochemical assays,
molecular biology, immunology and in vitro and in vivo infection
models (tissue cultures and rodent models).
Postdoctoral Positions Available
Please inquire directly.
Publications
Selected Publications
Anjali Mandlik, Arlene Swierczynski, Asis Das and Hung
Ton-That. (2008) Pilus assembly in Gram-positive bacteria and
function in colonization and biofilm development. Trends in
Microbiology, 16(1):33-40.
Anu Swaminathan*, Anjali Mandlik*, Arlene Swierczynski,
Andrew Gaspar, Asis Das and Hung Ton-That. (2007) Housekeeping
sortase facilitates the cell wall anchoring of pilus polymers in
Corynebacterium diphtheriae. Molecular Microbiology,
66(4): 961–974.
Vengadesan Krishnan†, Andrew H. Gaspar†, Naiqing Ye, Anjali
Mandlik, Hung Ton-That*, and Sthanam V L Narayana*. (2007) An
IgG-like domain in the minor pilin GBS52 of Streptococcus
agalactiae mediates lung epithelial cell adhesion. Structure,
15(8):893–903.
Anjali Mandlik, Arlene Swierczynski, Asis Das and Hung
Ton-That. (2007) Corynebacterium diphtheriae employs specific
minor pilins to target human pharyngeal epithelial cells.
Molecular Microbiology, 64(1):111-24.
Arunima Mishra, Asis Das, John O. Cisar and Hung Ton-That.
(2007) Sortase-catalyzed assembly of distinct heteromeric
fimbriae in Actinomyces naeslundii. Journal of Bacteriology,
189(8):3156-65.
Arlene Swierczynski and Hung Ton-That (2006) Type III pilus
of corynebacteria: Pilus length is determined by the level of
its major pilin subunit. Journal of Bacteriology,
188(17):6318-25.
Andrew H. Gaspar and Hung Ton-That. (2006) The Assembly of
Distinct Pilus Structures on the Surface of Corynebacterium
diphtheriae. Journal of Bacteriology, 188(4):
1526-33.
Andrew H. Gaspar, Luciano A. Maraffini, Hung Ton-That,
and Olaf Schneewind. (2005) Bacillus anthracis sortase A
(SrtA) anchors LPXTG motif containing surface proteins to the
cell wall envelope. Journal of Bacteriology, 187
(13):4646-55.
Hung Ton-That, Luciano A. Maraffini, and Olaf Schneewind.
(2004) Protein Sorting to the Cell Wall Envelope of
Gram-positive Bacteria. Biochimica et Biophysica Acta,
1694: 269-278.
Hung Ton-That, Luciano A. Maraffini, and Olaf Schneewind.
(2004) Sortases and Pilin Elements Involved in Pilus Assembly of
Corynebacterium diphtheriae. Molecular Microbiology,
53(1):251-261
Hung Ton-That and Olaf Schneewind (2004) Pilus
Assembly in Gram-positive Bacteria. Trends in Microbiology,
12(5):228-234
Hung Ton-That and Olaf Schneewind. (2003) Assembly of
Pili on the Surface of Corynebacterium diphtheriae. Molecular
Microbiology, 50(4):1429-1438.
 View more publications, see
Pubmed listing.
Revised April, 2008. |
