Structural studies of Vibrio cholerae quorum sensing proteins
Abstract
The spread of cholera is always associated with contaminated food or water
and this is the reason this disease has been endemic in developing countries
for centuries due to their lack of proper sanitation facilities and poor or no
infrastructure for sewage systems. Cholera can spread quickly and
sporadically after any natural disaster that destroys the sewage system or
safe drinking water supply of both developed and undeveloped countries. In
Southeast Asia in December 2004 and in Pakistan and Haiti 2010, cholera
outbreaks followed the natural disasters; with most of the cholera victims
being children. Although it is known that the best way to prevent cholera
outbreak is the development of the infrastructure, provision of a safe drinking
water supply and proper sanitation, this is a very long-term process, and most
of the developing countries cannot afford such improvements. These
situations can be made worse by natural disasters. Therefore there is a
pressing need for the development of a cholera vaccine and there have been
numerous research projects working towards this end for several decades. A
few of them have been successful to date but because of the severe side
effects and narrow range of protection, more effective and wider range
vaccine development is still ongoing.
In this study, crystallographic and enzymatic studies have been carried out on
several novel proteins involved in the control of the production of the factors
required for quorum sensing. Quorum sensing is a process in which bacterial
cells communicate among themselves by the synthesis, release and detection
of small chemical compounds called autoinducers. In this work, structural analysis was carried out on proteins involved in the synthesis and detection of
the major autoinducer of Vibrio cholerae, named CAI-1. The crystal structure
of CqsA involved in CAI-1 synthesis has been successfully solved and its
enzymatic properties have been characterized. The structure of one domain
of the cytoplasmic region of the CAI-1 receptor CqsS was also elucidated, and
other domains were expressed. The crystal structure of another enzyme
(VCA0859, an aldo-keto reductase) thought to have been involved in the
synthesis of CAI-1 was also determined. Another protein named VCA0939
was also studied, due to its importance in biofilm development, and its ability
to control quorum-sensing in an alternative pathway in the mutated version of
pathogenic strains of V. cholerae that were responsible for the seventh
cholera pandemic. The aim of this project was to understand the three
dimensional structure of some proteins that are involved in quorum sensing
and control of the expression of virulence genes for the pathogenesis of V.
cholerae. Understanding the three dimensional structure of the proteins and
the mode of autoinducer binding to its specific receptor could be highly
valuable in the development of a chemical compound that could lead to the
discovery of a novel drug with the ability to target cross species specification.
Type
Thesis, PhD Doctor of Philosophy
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