Tachyplesin I (TPI) is an antimicrobial polypeptide originally detected in Japanese Horse Shoe Crab.
The antimicrobial activity of the peptide is closely related to the composition of the pathogen membrane and ability of the peptide to permeabilize the cell membranes. Bacteria and fungi have negatively charged membranes, and the interaction of is mediated in large part by electrostatic interactions[1] (you can see the Hydrophobic and Polar amino acids).
It shows high affinity for lipopolysaccharides (LPS) of gram-negative bacteria, thus neutralizing its effects. It has also been reported to inhibit the growth of gram positive bacteria, fungui and viruses.
Structural highlights
The amino acid sequence of the TPI is NH₂-Lys-Trp-Cys-Phe-Arg-Val-Cys-Tyr-Arg-Gly-Ile-Cys-Tyr-Arg-Arg-Cys-Arg-CONH₂.
It adopts antiparallel β-sheet (hairpin) conformation in solution stabilized by two cross-strand between Cys³-Cys¹⁶ and Cys⁷-Cys¹², and its C-terminus is amidated.[1][2]
Image:Scheme.jpg
Tachyplesin is highly stable at low pH and high temperature. [3]
Besides, there exists H-bond and aromatic ring stacking interactions which helps stabilizing the hairpin loop structure of the peptide.
There are three linear derivatives of TPI: , TPF4 and TPA4.
Image:Derivatives.jpg
Since linear tachyplesin analogues do not show preferential affinity for LPS, the hairpin properties of the peptide seems to be important for recognition of lipopolysaccharides and its biological activities.
TPI undergoes confirmation change in . The backbone of the polypeptide becomes , making it more stable.
Mode of action
TPI can bind to LPS and also has ability to permeabilize the cell membrane of pathogens. Docking model suggests strong affinity to LPS gained by interaction between cationic residues of TPI with phosphate group and sachharides of LPS. Furthermore, interaction between hydrophobic residues of TPI with acyl chains of LPS strengthens the TPI/LPS interaction. The binding of TPI to LPS neutralizes LPS, which is widely considered as endotoxin. In addition to LPS binding, footpriting analysis has revealed the binding of TPI to DNA by interacting specifically in minor groove of DNA duplex. The interaction between TPI and DNA is contributed by secondary structure of the peptide which contains an antiparallel beta-sheet constrained by two disulfide bridges and connected by β-turn.
Importance and relevance
Evidences suggest that TPI has ability to permeabilize the cell membranes of pathogens.[1]. Also, LPS and DNA being the potential biological targets of the peptide, its antimicrobial activity might be exploited. Eyeing the potential of TPI, it has been insetred successfully in genome of Ornithogalum dubium and Ornithogalum thyrsoides. These ornamentals plants were originally sensitive to soft rot erwinias (SREs) and insertion of TPI in the plants has successfully protected them without affecting their normal physiology.
Function
This is a sample scene created with SAT to by Group, and another to make of the protein. You can make your own scenes on SAT starting from scratch or loading and editing one of these sample scenes.
