Tachyplesin I (TPI) is an antimicrobial polypeptide originally detected in Japanese Horse Shoe Crab.
The antimicrobial activity of peptides is closely related to the composition of the pathogen membrane. Bacteria and fungi have negatively charged membranes, and the interaction of cationic peptides such as tachyplesin I is mediated in large part by electrostatic interactions.[1]
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 aminoacid sequence of the TPI is H-Lys-Trp-Cys-Phe-Arg-Val-Cys-Tyr-Arg-Gly-Ile-Cys-Tyr-Arg-Arg-Cys-Arg-NH₂ with between Cys³ and Cys¹⁶/Cys⁷ and Cys¹².
Image:Scheme.jpg
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: , TPF4 and TPA4.
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 more rigid and twisted in presence of LPS, than in the , making it more stable.
Importance
The activity of Tachyplesin I is derived from its ability to permeabilize the cell membranes of pathogens.
Relevance
Function
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