Team:Fatih Turkey/LALF

Lipopolysaccharide (LPS), or endotoxin, is the major mediator of septic shock, a serious complication of Gram-negative bacterial infections in humans. Molecules that bind LPS and neutralize its biological effects or enhance its clearance could have important clinical applications. Limulus anti-LPS factor (LALF) binds LPS tightly, and, in animal models, reduces mortality when administered before or after LPS challenge or bacterial infection. The wedge-shaped molecule has a striking charge distribution and amphipathicity that suggest how it can insert into membranes. The binding site for LPS probably involves an extended amphipathic loop, and it has been proposed that two mammalian LPS-binding proteins will have a similar loop. The amphipathic loop structure may be used in the design of molecules with therapeutic properties against septic shock.

Horseshoe crabs (Limulus polyphemus and Tachypleus tridentatus) are ancient arachnids that possess a primitive circulatory system, the hemolymph, containing only one kind of cell, the hemocyte. Exposure of hemocytes to bacterial endotoxins [lipopolysaccharide (LPS)] results in the activation of an intracellular coagulation cascade (Iwanaga et al., 1986), a defense against microbial invasion. The system consists of several proteins, including one that may inhibit the cascade, called anti-LPS factor(Morita et al., 1985). Limulus anti-LPS factor (LALF) is a small (101 amino acids), basic protein (Aketagawa et al., 1986; Muta et al., 1987), which binds and neutralizes LPS (Wainwright et al., 1990) and has a strong anti-bacterial effect on the growth of Gram-negative R-type bacteria (Morita et al., 1985)(22). Our interest in determining the crystal structure of LALF arose from its potential in designing molecules that would have therapeutic properties in humans. It has been proposed that LALF has sequence similarity with ct-lactalbumin, a protein that binds LPS in vitro (Aketagawa et al., 1986).

LALF recognizes the lipid A portion of individual soluble LPS molecules (Warren et al., 1992), which are obtained below the critical micellar concentration. The simplest molecules that bind lipid A with high affinity are the polymyxin family of antibiotics; these are positively charged amphipathic cyclic oligopeptides linked to a single fatty acid (Morrison and Jacobs, 1976).

Endotoxin-neutralizing protein protects against Endotoxin-Induced Endothelial Barrier Dysfunction. Endotoxin-neutralizing protein, a recombinant peptide that is derived from Limulus antilipopolysaccharide factor and targets lipid A, could block the effects of lipopolysaccharide on protein tyrosine phosphorylation, actin organization, and movement of 14C-bovine serum albumin across bovine pulmonary artery endothelial cell monolayers. endotoxin-neutralizing protein crossprotected against lipopolysaccharide derived from diverse gram-negative bacteria. LALF is a 11.8-kDa protein isolated from the amebocyte, the single blood cell type found in the horseshoe crab (13). The amebocyte-derived LALF as well as its recombinant form, endotoxin-neutralizing protein (ENP), each binds to and neutralizes LPS (13, 18). The LPS-binding site is 32 to 50 amino acids in length and forms an amphipathic loop which binds to the lipid A portion of LPS (11, 15, 18). We therefore studied whether a molecule such as ENP, which binds to lipid A and has been shown to confer protection against the deleterious effect of LPS in vivo, could block one or more of the sequential LPS-induced events leading to increased EC monolayer permeability. In this work, we have studied whether ENP protects against LPS-induced protein tyrosine phosphorylation, actin reorganization, and loss of endothelial barrier function. the importance of the amphipathic loop structure can be investigated by introducingappropriate disulfide bonds to create a cyclic conformation. However, previous investigations with cysteine- and non-cysteine- containing peptides derived from TALF, a protein highly homologous with LALF, showed little difference in LPS binding activity (23).

Considering that Limulus anti-lipopolysaccharide factor (LALF) reduces the growth of gram negative bacteria and terminates them; we determine that it can be used as a surface protector. In our Project, we plan to design LALF protein producing system in specific bacteria that will not be harmed by this bactericide itself. To do this, we needed a bacteria type that has no lip-A structure which is bound by LALF. Thus, we decided to use Bacillus subtilis colonies which are the most prefered gram positive bacteria in iGEM. In conclusion, our “protector” bacteria affects on E. Coli mortally, therefore our remaining region is cleared from E.coli. As a future aspect, a special covering material, a biofilm for example, may be used as a cover sheet on surfaces that leads to protection of bacterias.

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