Plant lipid transfer proteins
|Plant lipid transfer protein|
Plant lipid transfer proteins, also known as plant LTPs or PLTPs, are a group of highly-conserved proteins of about 7-9kDa found in higher plant tissues. As its name implies, lipid transfer proteins are responsible for the shuttling of phospholipids and other fatty acid groups between cell membranes. LTPs are divided into two structurallyrelated subfamilies according to their molecular masses: LTP1s (9 kDa) and LTP2s (7 kDa). Various LTPs bind a wide range of ligands, including fatty acids (FAs) with a C10–C18 chain length, acyl derivatives of coenzyme A (CoA), phospho- and galactolipids, prostaglandin B2, sterols, molecules of organic solvents, and some drugs. LTP2
LTPs constitute one of the classes of defense PRPs, many of which have antimicrobial and enzymatic activities or are enzyme inhibitors. Different proteins of this class can exhibit the following activities:
and inhibit some enzymes.
Ordinarily, most lipids do not spontaneously exit membranes because their hydrophobicity makes them poorly soluble in water. LTPs facilitate the movement of lipids between membranes by binding, and solubilising them. LTPs typically have broad substrate specificity and so can interact with a variety of different lipids.
LTPs in plants may be involved in:
- cutin biosynthesis
- surface wax formation
- mitochondrial growth
- pathogen defense reactions
- adaptation to environmental changes
- lipid metabolism
- fertilization of flowering plants
- adaptation of plants under stress conditions
- activation and regulation of signaling cascades
- fruit ripening
Plant lipid transfer proteins consist of 4 alpha-helices in a right-handed superhelix with a folded leaf topology. The structure is stabilised by disulfide bonds linking the helices to each other.
The structure forms an internal hydrophobic cavity in which 1-2 lipids can be bound. The outer surface of the protein is hydrophilic allowing the complex to be soluble. The use of hydrophobic interactions, with very few charged interactions, allows the protein to have broad specificity for a range of lipids.
Plant lipid transfer proteins share the same structural domain with seed storage proteins and trypsin-alpha amylase inhibitors. These proteins share the same superhelical, disulphide-stabilised four-helix bundle containing an internal cavity.
There is no sequence similarity between animal and plant LTPs. In animals, cholesterylester transfer protein (CETP), also called plasma lipid transfer protein, is a plasma protein that facilitates the transport of cholesteryl esters and triglycerides between the lipoproteins.
Role in human health
PLTPs are pan-allergens,   and may be directly responsible for cases of food allergy. Pru p 3, the major allergen from peach, is a 9-kDa allergen belonging to the family of lipid-transfer proteins.  Allergic properties are closely linked with high thermal stability and resistance to gastrointestinal proteolysis of the proteins. Many of the LTP allergens are able to cause not only manifestation of allergic reactions but also sensitization via the gastrointestinal tract, being thus class I food allergens. In contrast, class II food allergens are able only to elicit allergic symptoms due to its cross-reactivity with major sensitizer.
They are used as antioxidants and prevent diseases.
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