Arthropod defensin
Encyclopedia
Arthropod defensins are a family of insect and scorpion cysteine
-rich antibacterial peptides, primarily active against Gram-positive bacteria. All these peptides range in length from 38 to 51 amino acids. There are six conserved cysteines all involved in intrachain disulfide bonds.
A schematic representation of peptides from the arthropod defensin
family is shown below.
+----------------------------+
| |
xxCxxxxxxxxxxxxxxCxxxCxxxxxxxxxCxxxxxCxCxx
| | | |
+---|---------------+ |
+-----------------+
'C': conserved cysteine involved in a disulfide bond.
Although low level sequence similarities have been reported between the arthropod defensins and mammalian defensins, the topological arrangement of the disulfide bond
s as well as the tertiary structure
are completely different in the two families.
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
-rich antibacterial peptides, primarily active against Gram-positive bacteria. All these peptides range in length from 38 to 51 amino acids. There are six conserved cysteines all involved in intrachain disulfide bonds.
A schematic representation of peptides from the arthropod defensin
Defensin
Defensins are small cysteine-rich cationic proteins found in both vertebrates and invertebrates. They have also been reported in plants. They are, and function as, host defense peptides. They are active against bacteria, fungi and many enveloped and nonenveloped viruses. They consist of 18-45 amino...
family is shown below.
+----------------------------+
| |
xxCxxxxxxxxxxxxxxCxxxCxxxxxxxxxCxxxxxCxCxx
| | | |
+---|---------------+ |
+-----------------+
'C': conserved cysteine involved in a disulfide bond.
Although low level sequence similarities have been reported between the arthropod defensins and mammalian defensins, the topological arrangement of the disulfide bond
Disulfide bond
In chemistry, a disulfide bond is a covalent bond, usually derived by the coupling of two thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore R-S-S-R. The terminology is widely used in biochemistry...
s as well as the tertiary structure
Tertiary structure
In biochemistry and molecular biology, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.-Relationship to primary structure:...
are completely different in the two families.
Further reading
- Refined three-dimensional solution structure of insect defensin A. CornetB, Bonmatin JM, Hetru C, Hoffmann JA, Ptak M, Vovelle F; Structure 1995;3:435-448.