Hank
S. Seifert, PhD
Professor
Department of Microbiology-Immunology
To Contact Dr. Seifert:
phone:312-503-9788
e-mail: h-seifert@northwestern.edu
Dr. Seifert's website
PubMed
Reference Lookup
Research Interests
The laboratory of Dr. Seifert studies the pathogenesis of Neisseria
gonorrhoeae with a concentration on the pilus. This major virulence factor
mediates the initial attachment of the bacterium to host epithelial cells
and undergoes antigenic variation in order to help the pathogen escape the
host immune system. There is no documented natural immunity to gonococcal
infection. This is partly due to the enormous potential N. gonorrhoeae has
for antigenic variation of surface proteins. N. gonorrhoeae has the ability
to express numerous antigenically distinct pilin proteins. This occurs when
silent pilin sequences, which are found in distinct loci throughout the chromosome,
recombine into the singular expression locus. The primary mechanism used by
the bacterium to catalyze antigenic variation has been described as gene conversion,
or intragenomic, nonreciprocal DNA recombination. They are using a variety
of molecular biological, genetic, and biochemical techniques to investigate
the molecular mechanisms controlling gonococcal DNA recombination, to describe
the process of pilin variation in human hosts, and to determine the effect
of changes of pilin sequence on pilus structure and function. There is only
one natural ecological niche for this organism, people, and the variation
produced in this organelle is essential for the propagation of this species
within human populations and the production of disease.
Dr. Seifert’s laboratory
is elucidating the mechanisms used to mediate and control pilin antigenic
variation. This includes genetics screening to identify proteins involved
in the process, directed mutagenesis of genes from the gonococcal genome that
may be involved in these recombination processes, and sites within the pilin
loci that play a role in the recombination processes. They have shown that
the frequency of pilin antigenic variation is regulated by iron availability
and they are determining how and when during infection this regulation occurs.
They are also interested
in how the pilus functions in cell adherence, DNA transformation, and twitching
motility. His lab is using genetic approaches coupled with fluorescent and
electron microscopy to determine how the pilus functions as an organelle.
They have evidence that the pilus assembly apparatus, and not the pilus fiber,
is mediating the transport of DNA into the cytoplasm for transformation. His
lab has also correlated spectinomycin resistance with the pilus assembly apparatus
and postulate that it is also involved in transporting this antibiotic.
Central to pilin variations
and DNA transformation is the RecA protein. Dr. Seifert’s laboratory
is carrying out a detailed structure/function study by following the differences
expressed between the gonococcal and E. coli RecA proteins when expressed
in gonococci. While the E. coli protein functions well as a recombinase during
DNA transformation in gonococci, it does not participate at all in DNA repair
and exhibits greatly increased frequencies of pilin variation. By constructing
hybrid proteins between the E. coli and gonococcal RecAs, determining whether
biochemical differences exist between these homologues, and finding proteins
partners of these RecA homologues they are determining how these proteins
act during DNA transformation, DNA repair and pilin variation.
Lastly, Dr. Seifert’s
lab is taking advantage of the recent completion of the first gonococcal genome
sequence to begin improvement of genetic methods to utilize in whole genome
investigations and the use of bacterial arrays. The development of these tools
will help their studies of gonococcal biology along with those of other laboratories
studying these organisms.