Structure and function of LanC-like proteins

The research project "Structure and function of LanC-like proteins" deals with the biochemical, molecular and cell biological investigation of a new red cell protein, LANCL1, which is similar to the bacterial LanC proteins. The LanC proteins are subunits of a high molecular weight enzymatic complex, which synthesizes antimicrobial, so- called "lantibiotic" peptides. These peptides defend the bacteria against overgrowth by other microorganisms. This antimicrobial effect has also an economic significance, because lantibiotic peptides are being used as natural preservatives in food industry for more than 50 years. However, it is unknown whether the human organism is capable of synthesizing similar peptides. The presently known human peptides of the innate immune system show similar, but clearly different structures. Interestingly, LANCL1 is not only expressed in red cells, but also in neurons of the brain, in testis, several cell types of the immune system, and in the epithelia of gut and lung. Most of these tissues and cell types also contain human antimicrobial peptides. In this project, the structure and function of LANCL1 and its homologue LANCL2 shall be determined. Questions will be studied whether these proteins are subunits of an enzymatic complex, whether they interact with prepeptides thereby synthesizing antimicrobial peptides, and whether they associate with a peptide transporter. Moreover, the type of peptide modification shall be investigated. It is conceivable that this information can be used for the synthesis of new antibiotic drugs.

In the project P15786 "Structure and function of LanC-like proteins" we investigated two relatively unknown proteins, LANCL1 and LANCL2. These proteins show a structural similarity to the bacterial LanC-proteins that play a role in the biosynthesis of anti-bacterial peptides (lantibiotics). Therefore, we thought that the human LANCL proteins might be involved in the immune system, however, this could not be verified yet. In this project, we characterized both proteins with biochemical and cell biological methods. Moreover, we expressed and purified these proteins for structural analyses and we identified interacting proteins. We characterized LANCL1 as a novel glutathione-binding, oxidation-sensitive, cytoplasmic protein that sensitises the cell to cytotoxic drugs. This protein may have a function in the regulation of multi drug resistance to cytotoxic substances some of which are exploited as anti-cancer drugs. Because LANCL1 was recently found to play an important role in malaria infection of red cells, it could also serve as a target for anti-malaria drugs. In contrast to the cytosolic LANCL1, we characterized LANCL2 as a membrane protein modified by the fatty acid, myristic acid. Such myristoylated proteins are found in signalling cascades of the cell that are assembled at cholesterol-rich microdomains of the plasma membrane. LANCL2 also binds to phosphatidylinositol phosphates (PIPs), lipids that play an important role in cell signalling. PIPs are essential for the regulation of the cytoskeleton and for the growth of the cell in general. LANCL2 expression sensitises the cells to cytotoxic substances. This sensitivity is dependent on the membrane association of LANCL2. A LANCL2 mutant that could not bind to the plasma membrane but was found in the nucleus had no effect on the sensitivity to cytotoxic drugs. When we studied LANCL2-interacting proteins, we identified two proteins, a heat shock protein of the Hsp70 family, and a glycolytic enzyme, alpha-enolase. Both proteins are known inhibitors of myristoylation and targets for anti-cancer drugs. Possibly, these proteins may be up-regulated in a response to the LANCL2 overexpression. Our results were not foreseen in the original hypothesis, however, they provide valuable insights in the nature of these relatively unknown proteins and enable us now to ask more specific questions as to their structure and function.