Biology Reference
In-Depth Information
Chapter 16
Type 1 and 5 secretion systems
and associated toxins
Timothy J. Wells and Ian R. Henderson
University of Birmingham, Birmingham, UK
INTRODUCTION
Pathogenic
Escherichia coli
can cause disease in a variety of locations in the
human body. The site of infection is dependent on the repertoire of virulence
factors such as adhesins and toxins expressed by the pathogen. Most proteins
involved in virulence need to traverse both the inner and outer membrane of
the bacterium and in some cases the membrane of the host cell to perform their
function. Given the diversity of function, multitude of targets and variety of
structures of these secreted proteins, it is unsurprising to find that
E. coli
has
multiple different secretion systems to effect translocation of proteins to the
exterior of the cell.
Two of the simplest secretion systems that
E. coli
utilizes are the type 1
secretion system (T1SS) and the type 5 secretion system (T5SS). These secre-
tion systems are widely distributed in other Gram-negative bacteria. In
E. coli
the best-known T1SS is that used to secrete hemolysin, a pore-forming toxin
found in both uropathogenic (UPEC) and enterohemorrhagic (EHEC) strains
of
E. coli.
The T5SS is widespread in
E. coli
with many of the virulence factors
secreted by this mechanism specific for a particular pathotype. This chapter will
focus on the T1SS and T5SS; the mechanism of biogenesis, the function of the
secreted proteins and current attempts to use these systems in biotechnological
applications. Other
E. coli
secretion systems are discussed in detail in other
chapters.
THE TYPE 1 SECRETION SYSTEM
The T1SS of Gram-negative bacteria allows the secretion of proteins from the
cytoplasm to the extracellular environment in a single step, with no periplas-
mic intermediate (
Figure 16.1
). Proteins secreted by the T1SS greatly vary
in size, from 82 amino acids (aa) to over 8000 residues (
Delepelaire, 2004
).
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