1.C.34 The Tachyplesin (Tachyplesin) Family

The tachyplesins are β-structured protegrin-like molecules that are produced in horseshoe crab hemocytes. They are found in hemocyte S-granules and are active against Gram-negative and Gram-positive bacteria, fungi and enveloped viruses such as HIV. They form transient anion-selective pores in phospholipid bilayers in a process that is facilitated by the application of a cis-negative membrane potential. They are cross linked by disulfide bridges. Tachyplesin I is a cyclic β-sheet antimicrobial.

It can both form pores and translocate across acidic phospholipid membranes. It shows high affinity for lipopolysaccharides (LPS) from Gram-negative bacteria (300x higher affinity than for acidic phospholipids). Linear tachyplesin analogues do not show this preferential affinity for LPS suggesting that the cyclic properties are important for macromolecular recognition and the biological activities (Hirakura et al., 2002).

The generalized reaction catalyzed by tachyplesins is: 

Small molecules (in) Small molecules (out)