Antimicrobial peptides: Marine crustaceans’ weapon against diseases
Sue Hui Tan
Compared to us humans, marine crustaceans such as crabs and shrimps possess a simpler and
more basic immune system to protect themselves against disease-causing microorganisms. In
recent years, scientists have discovered an abundance of a particular group of molecules
called antimicrobial peptides (AMPs) in the body fluids of marine crustaceans, which are
believed to play an important role in their immune systems. As the name suggests, AMPs are
proteins that act against a broad range of bacteria by killing them. Due to the natural
antibiotic property of these molecules, substantial research has been carried out on
investigating their potential as therapeutic alternatives to current antibiotics. AMPs are also
promising measures for the prevention and cure of diseases that marine crustaceans are
susceptible to. This holds significant importance for fisheries and aquaculture all around the
world, since marine crustaceans like crabs and shrimps are important resources for these
industries.
Currently, AMPs from the shore crab and the Pacific white shrimp have been isolated and
investigated by researchers. By analyzing and comparing these proteins against other well
understood AMPs, knowledge of their properties and antimicrobial activities have been
deduced. Experiments have also been performed in laboratories to test the AMPs for activity
against different species of bacteria. However, due to the nature of the proteins, successful
detection of antimicrobial activity has proven elusive for many of the AMPs tested.
In this project, three DNA sequences coding for three different AMPs were isolated from the
freshwater signal crayfish. Using a bacterial expression system, these proteins were produced
in order to test them for antimicrobial activity. It was found that the proteins were not very
soluble and this posed difficulties in efficiently obtaining pure samples of them. Therefore,
only one AMP, called crustin 1, was eventually isolated, purified and used for further tests.
The crustin 1 protein produced in this experiment possess an additional protein portion which
is necessary for the isolation and purification processes. Following these procedures, attempts
were made to remove the extra protein segment from the crustin 1 protein, but it was
discovered that the amount of AMPs obtained after this procedure was too low to be used in
subsequent tests. Consequently, the tests for antimicrobial activity were performed using the
crustin 1 protein that carried the additional protein portion. However, this crustin 1 protein
failed to exhibit any antimicrobial activity against any of the species of marine bacteria used
in the tests. This absence of antimicrobial activity might be caused by the presence of the
extra protein segment that may prevent the crustin 1 protein from functioning properly, or
could also have been due to the amount of proteins used in the tests, which might have been
too low.
In spite of the results for the crustin 1 protein, more experiments should be performed to test
for the antimicrobial activities of the remaining two AMPs. Experimental techniques carried
out on the proteins should be modified so that they are optimal and more compatible for the
properties of the proteins. In this way, these AMPs might then be able to display
antimicrobial activity against bacteria in laboratory tests.
Degree project in biology
Examensarbete i biologi, 20 p, Uppsala universitet, höst 2006
Biology Education Centre and Department of Comparative Physiology, Uppsala University
Supervisor: Irene Söderhäll