plant lipid transfer proteins
{{Infobox protein family
|Symbol = LTP/seed_store/tryp_amyl_inhib
|Name = Plant lipid transfer protein / bifunctional inhibitor / seed storage protein, 4-helical domain
|image = File:Surface_1UVB.png
|caption = Oryza sativa Lipid Transfer Protein 1 bound to palmitic acid (black). Positive charge in blue; negative charge in red ({{PDB|1UVB}}).
|Pfam = PF00234
|Pfam_clan = CL0482
|InterPro = IPR016140
|SMART = SM00499
|SCOP = 1UVB
|CATH = 1UVB
|CDD = cd00010
|PDB = {{PDB|1UVB}} {{PDB|1afh}} {{PDB|1b1u}} {{PDB|1be2}} {{PDB|1bea}} {{PDB|1bfa}} {{PDB|1bip}} {{PDB|1bwo}} {{PDB|1cz2}} {{PDB|1fk0}} {{PDB|1fk1}}
|below = Also {{Pfam|PF13016}}, {{Pfam|no=1|PF14368}}; see the Pfam clan relationships.}}
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.{{cite journal |vauthors=Asero R, Mistrello G, Roncarolo D, de Vries SC, Gautier MF, Ciurana CL, Verbeek E, Mohammadi T, Knul-Brettlova V, Akkerdaas JH, Bulder I, Aalberse RC, van Ree R |date=2001 |title=Lipid transfer protein: a pan-allergen in plant-derived foods that is highly resistant to pepsin digestion |journal=International Archives of Allergy and Immunology |volume=124 |issue=1–3 |pages=67–9 |doi=10.1159/000053671 |pmid=11306929 |s2cid=40934840}}{{cite journal |vauthors=Finkina EI, Melnikova DN, Bogdanov IV, Ovchinnikova TV |title=Lipid Transfer Proteins As Components of the Plant Innate Immune System: Structure, Functions, and Applications |journal=Acta Naturae |volume=8 |issue=2 |pages=47–61 |date=2016 |pmid=27437139 |pmc=4947988 |doi=10.32607/20758251-2016-8-2-47-61}} As its name implies, lipid transfer proteins facilitate the shuttling of phospholipids and other fatty acid groups between cell membranes.{{cite journal |vauthors=Kader JC |date=June 1996 |title=Lipid-Transfer Protein in Plants |journal=Annual Review of Plant Physiology and Plant Molecular Biology |volume=47 |pages=627–654 |doi=10.1146/annurev.arplant.47.1.627 |pmid=15012303}} LTPs are divided into two structurally related subfamilies according to their molecular masses: LTP1s (9 kDa) and LTP2s (7 kDa).{{cite journal |vauthors=Finkina EI, Melnikova DN, Bogdanov IV, Ovchinnikova TV |date=2017-07-04 |title=Plant Pathogenesis-Related Proteins PR-10 and PR-14 as Components of Innate Immunity System and Ubiquitous Allergens |journal=Current Medicinal Chemistry |volume=24 |issue=17 |pages=1772–1787 |doi=10.2174/0929867323666161026154111 |pmid=27784212}} Various LTPs bind a wide range of ligands, including fatty acids with a C10–C18 chain length, acyl derivatives of coenzyme A, phospho- and galactolipids, prostaglandin B2, sterols, molecules of organic solvents, and some drugs.
The LTP domain is also found in seed storage proteins (including 2S albumin, gliadin, and glutelin) and bifunctional trypsin/alpha-amylase inhibitors.{{cite journal |vauthors=Lin KF, Liu YN, Hsu ST, Samuel D, Cheng CS, Bonvin AM, Lyu PC |title=Characterization and structural analyses of nonspecific lipid transfer protein 1 from mung bean |journal=Biochemistry |volume=44 |issue=15 |pages=5703–12 |date=April 2005 |pmid=15823028 |doi=10.1021/bi047608v |hdl=1874/385163 |hdl-access=free}}{{cite journal |vauthors=Pantoja-Uceda D, Bruix M, Giménez-Gallego G, Rico M, Santoro J |title=Solution structure of RicC3, a 2S albumin storage protein from Ricinus communis |journal=Biochemistry |volume=42 |issue=47 |pages=13839–47 |date=December 2003 |pmid=14636051 |doi=10.1021/bi0352217}}{{cite journal |vauthors=Oda Y, Matsunaga T, Fukuyama K, Miyazaki T, Morimoto T |title=Tertiary and quaternary structures of 0.19 alpha-amylase inhibitor from wheat kernel determined by X-ray analysis at 2.06 A resolution |journal=Biochemistry |volume=36 |issue=44 |pages=13503–11 |date=November 1997 |pmid=9354618 |doi=10.1021/bi971307m}}{{cite journal |vauthors=Gourinath S, Alam N, Srinivasan A, Betzel C, Singh TP |date=March 2000 |title=Structure of the bifunctional inhibitor of trypsin and alpha-amylase from ragi seeds at 2.2 A resolution |journal=Acta Crystallographica D |volume=56 |issue=Pt 3 |pages=287–93 |doi=10.1107/s0907444999016601 |pmid=10713515}} These proteins share the same superhelical, disulfide-stabilised four-helix bundle containing an internal cavity.
There is no sequence similarity between animal and plant LTPs. In animals, cholesteryl ester transfer protein, also called plasma lipid transfer protein, is a plasma protein that facilitates the transport of cholesteryl esters and triglycerides between the lipoproteins.
Function
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.{{cite journal |vauthors=Cheng HC, Cheng PT, Peng P, Lyu PC, Sun YJ |date=September 2004 |title=Lipid binding in rice nonspecific lipid transfer protein-1 complexes from Oryza sativa |journal=Protein Science |volume=13 |issue=9 |pages=2304–15 |doi=10.1110/ps.04799704 |pmc=2280015 |pmid=15295114}}
LTPs are known to be pathogenesis-related proteins, i.e. proteins produced for pathogen defense by plants. Some LTPs are known to be antibacterial, antifungal, antiviral, and/or in vitro antiproliferative. The enzyme inhibitor members are thought to regulate the development and germination of seeds as well as protect against insects and herbivores.
LTPs in plants may be involved in:
- cutin biosynthesis
- surface wax formation
- mitochondrial growth
- adaptation to environmental changes{{cite journal |last1=Kader |first1=Jean-Claude |date=February 1997 |title=Lipid-transfer proteins: A puzzling family of plant proteins |journal=Trends in Plant Science |volume=2 |issue=2 |pages=66–70 |doi=10.1016/S1360-1385(97)82565-4}}
- lipid metabolism
- fertilization of flowering plants
- adaptation of plants under stress conditions
- activation and regulation of signaling cascades
- apoptosis
- symbiosis
- fruit ripening
Structure
{{Multiple image
|footer =Oryza sativa Lipid Transfer Protein 1 bound to palmitic acid. ({{PDB|1UVB}})
|align =right
|image1 =Cartoon_1UVB.png
|width1 =200
|caption1=Structure of OsLTP1 (white) bound to palmitic acid (black). Disulfide bridges indicated in yellow.
|image2 =Uncut_1UVB.png
|width2 =200
|caption2=Surface charge distribution. Positive charge in blue; negative charge in red.
|image3 =Cut 1UVB.png
|width3 =200
|caption3=Cut-through showing internal charge distribution. Positive charge in blue; negative charge in red.
}}
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 bridges 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.
Role in human health
PLTPs are pan-allergens,{{cite web |first=Adrian |last=Morris |name-list-style=vanc |url=https://www.allergy-clinic.co.uk/allergies/food-allergy/food-allergy-guide/ |title=Food Allergy in Detail |work=Surrey Allergy Clinic }}{{InterPro|IPR000528}} 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.{{cite journal |first1=Matthias |last1=Besler |first2=Javier Cuesta |last2=Herranz |first3=Montserrat |last3=Fernández-Rivas |name-list-style=vanc |journal=Internet Symposium on Food Allergens |volume=2 |issue=4 |pages=185–201 |year=2000 |url=http://www.food-allergens.de/symposium-2-4/peach/peach-allergens.htm |title=Peach allergy}} Allergic properties are closely linked with high thermal stability and resistance to gastrointestinal proteolysis of the proteins.{{cite journal |vauthors=Bogdanov IV, Shenkarev ZO, Finkina EI, Melnikova DN, Rumynskiy EI, Arseniev AS, Ovchinnikova TV |date=April 2016 |title=A novel lipid transfer protein from the pea Pisum sativum: isolation, recombinant expression, solution structure, antifungal activity, lipid binding, and allergenic properties |journal=BMC Plant Biology |volume=16 |pages=107 |doi=10.1186/s12870-016-0792-6 |pmc=4852415 |pmid=27137920 |doi-access=free }} They are class 1 (gastrointestinal) food allergens that cause a more systemic response than class 2 (respiratory) allergens.
Plant LTPs are considered antioxidants in a small subset of researches.{{cite journal |vauthors=Halliwell B |date=1996 |title=Antioxidants in human health and disease |journal=Annual Review of Nutrition |volume=16 |pages=33–50 |doi=10.1146/annurev.nu.16.070196.000341 |pmid=8839918}} Whether this has value for human health is unknown.
Commercial importance
Lipid transfer protein 1 (from barley) is responsible, when denatured by the mashing process, for the bulk of foam which forms on top of beer.{{cite web |url=http://www.crc.dk/flab/foam.htm |title=Foam |work=Carlsberg Research Laboratory |access-date=2009-03-05 |url-status=dead |archive-url=https://web.archive.org/web/20160303195030/http://www.crc.dk/flab/foam.htm |archive-date=2016-03-03}}