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Characterization of the antimicrobial peptide family defensins in the Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus), and tammar wallaby (Macropus eugenii)


Elizabeth A. Jones1 & Yuanyuan Cheng1 & Denis O’Meally1,2 & Katherine Belov1

1 Faculty of Veterinary Science, School of Life and Environmental Sciences, University of Sydney, Camperdown, NSW 2006, Australia
2 Centre for Animal Health Innovation, University of the Sunshine Coast, Sippy Downs, QLD 4556, Australia


Abstract

Defensins comprise a family of cysteine-rich antimicrobial peptides with important roles in innate and adaptive
immune defense in vertebrates. We characterized alpha and
beta defensin genes in three Australian marsupials: the
Tasmanian devil (
Sarcophilus harrisii), koala (Phascolarctos
cinereus
), and tammar wallaby (Macropus eugenii) and identified 48, 34, and 39 defensins, respectively. One hundred and
twelve have the classical antimicrobial peptides characteristics
required for pathogen membrane targeting, including cationic
charge (between 1+ and 15+) and a high proportion of hydrophobic residues (>30%). Phylogenetic analysis shows that
gene duplication has driven unique and species-specific expansions of devil, koala, and tammar wallaby beta defensins
and devil alpha defensins. Defensin genes are arranged in
three genomic clusters in marsupials, whereas further duplications and translocations have occurred in eutherians resulting
in four and five gene clusters in mice and humans, respectively. Marsupial defensins are generally under purifying selection, particularly residues essential for defensin structural stability. Certain hydrophobic or positively charged sites, predominantly found in the defensin loop, are positively selected,
which may have functional significance in defensin-target interaction and membrane insertion.
Keywords Tasmanian devil . Koala . Tammar wallaby .
Defensin . Evolution
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