Protein-antibiotic
Scientists have determined the structure of an antibacterial protein in platypus milk
Daria Spasskaya, N+1
The main protein of platypus milk – MLP protein – has a unique structure, unlike the known types of protein chain stacking, Australian scientists found out after deciphering the protein structure by X-ray diffraction analysis. The MLP protein was found only in the milk of platypus and echidna and has an antibacterial effect. The study was published in the journal Structural Biology Communications (section of the journal Acta Crystallographica).
The system of milk production in oviparous mammals, which include platypuses and echidnas, is very different from that of other mammals and is much more primitive. In particular, "advanced" mammals have nipples that allow the cubs to receive milk more efficiently and sterically. Platypuses have no nipples, and milk is released from the mammary glands simply to the surface of the skin in the abdominal area, from where the cubs have to lick it off. Probably for this reason, the composition of the milk of platypuses differs significantly from the milk of other mammals.
Earlier, Australian researchers showed that the milk of platypus and echidna has an antibacterial effect and destroys several types of pathogenic microorganisms, in particular, Staphylococcus aureus. As it turned out, the MLP (monotreme lactation protein) protein, which is enriched with milk, is responsible for the antibacterial effect.
Employees of the Biomedical Department of the State Association of Scientific and Applied Research of Australia (CSIRO) have developed a system for the expression of MLP protein in mammalian cells, isolated it and determined the protein structure using X-ray diffraction analysis with a resolution of 1.82 angstroms.
Three-dimensional structure of the MLP protein
Janet Newman et al / Structural Biology Communications 2018
As it turned out, MLP is a monomer consisting of 12 alpha helices with two small beta layers. A comparison of its three-dimensional structure with a database of known protein structures showed that MLP has a new, previously unknown type of stacking. The researchers tested the activity of the isolated protein in an antimicrobial activity test and confirmed its full functionality.
Despite the fact that egg-laying milk contains other proteins with antibacterial properties characteristic of all mammals, for example, lactoferrin and lysozyme, MLP is present exclusively in the "primitive" milk of platypus and echidna. Perhaps determining the structure of MLP will help to detect previously unknown vulnerabilities in staphylococcal cells, which are known for their ability to develop resistance to a wide range of antibiotics, and to develop new drugs to combat resistant bacteria.
In addition to the unusual composition of milk, platypuses have many unique features – for example, they are poisonous and have organs of electroreception.
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