1.C.47 The Insect/Fungal Defensin (Insect/Fungal Defensin) Family

Many insect (arthropod) defensins have been sequenced and shown to form ion channels in artificial membranes. Their precursor proteins are secreted and digested to the active peptides that can be bacterocidal and toxic to specific eukaryotic cells (Kourie and Shorthouse, 2000).

The defensins with a conserved cysteine-stabilized alpha-helix and beta-sheet (CSαβ) structural motif are a group of unique antimicrobial polypeptides widely distributed in plants and animals. Recently, one defensin-like peptide (DLP) with high degrees of sequence and structural similarity to defensins from ancient arthropods and molluscs has been identified in a saprophytic fungus (Mygind et al., 2005). This poses an important question regarding the evolutionary relationships of this class of effectors of innate immunity in three eukaryotic kingdoms.

Zhu (2008) reported the computational identification of six families of fungal DLPs in which three known defensin types (antibacterial ancient invertebrate-type defensins (AITDs), antibacterial classical insect-type defensins (CITDs), and antifungal plant/insect-type defensins (PITDs)) were clearly assigned. Sharing of these defensin types between animals and fungi supported their closer evolutionary relationship, consistent with the Opisthokonta Hypothesis. Conservation of the PITDs across three eukaryotic kingdoms suggests an earlier origin (Zhu, 2008).

The generalized transport reaction catalyzed by defensins is:

ions and small molecules (in) ions and small molecules (out)


This family belongs to the Defensin Superfamily.
 

References:

Kourie, J.I. and A.A. Shorthouse (2000). Properties of cytotoxic peptide-formed ion channels. Am. J. Physiol. Cell Physiol. 278: C1063-C1087.
Mygind, P.H., R.L. Fischer, K.M. Schnorr, M.T. Hansen, C.P. Sönksen, S. Ludvigsen, D. Raventós, S. Buskov, B. Christensen, L. De Maria, O. Taboureau, D. Yaver, S.G. Elvig-Jørgensen, M.V. Sørensen, B.E. Christensen, S. Kjaerulff, N. Frimodt-Moller, R.I. Lehrer, M. Zasloff, and H.H. Kristensen. (2005). Plectasin is a peptide antibiotic with therapeutic potential from a saprophytic fungus. Nature 437: 975-980.
Zhu, S. (2008). Discovery of six families of fungal defensin-like peptides provides insights into origin and evolution of the CSalphabeta defensins. Mol Immunol 45: 828-838.
Examples:

TC#NameOrganismal TypeExample
1.C.47.1.1Defensin precursor Insects Defensin precursor of Drosophila melanogaster
 
1.C.47.1.2Phormicin precursor Insects Phormicin precursor of Protophormia terraenovae
 
1.C.47.1.3Sapecin precursor Insects Sapecin precursor of Sarcophaga peregrina
 
1.C.47.1.4Tenecin precursor Insects Tenecin precursor of Tenebrio molitor
 
1.C.47.1.5

Soft tick Defensin A (73aas; 1 TMS)

Arachnids

Defensin A of Ornithodoros moubata (Q9BLJ3)

 
Examples:

TC#NameOrganismal TypeExample
1.C.47.2.1

L-Plectasin (40aas, 1 TMS); precursor (90aas, 2 TMSs). 3-d structure known (3E7R_L; 1ZFUA) (Mygind et al., 2005; Zhu, 2008) (43% identical to 1.C.47.1.1).

Fungi

L-Plectasin precursor of Pseudoplectania nigrella (Q53I06)