This entry includes a group of oil body associated proteins (OBAPs) from plants and some uncharacterised proteins from fungi and bacteria. The plant obap proteins are predominantly expressed during embryo development and may be involved in the stability of oil bodies [
].
Oleosins [
] are the proteinaceous components of plants' lipid storage bodiescalled oil bodies. Oil bodies are small droplets (0.2 to 1.5 mu-m in diameter)
containing mostly triacylglycerol that are surrounded by a phospholipid/oleosin annulus. Oleosins may have a structural role in stabilising the lipid
body during dessication of the seed, by preventing coalescence of the oil.They may also provide recognition signals for specific lipase anchorage in
lipolysis during seedling growth. Oleosins are found in the monolayer lipid/water interface of oil bodies and probably interact with both the lipid and
phospholipid moieties.Oleosins are proteins of 16 Kd to 24 Kd and are composed of three domains: an
N-terminal hydrophilic region of variable length (from 30 to 60 residues); acentral hydrophobic domain of about 70 residues and a C-terminal amphipathic
region of variable length (from 60 to 100 residues). The central hydrophobicdomain is proposed to be made up of β-strand structure and to interact with
the lipids []. It is the only domain whose sequenceis conserved.
This entry includes a group of plant glycerolipid A1 lipases, including PLIP1/2/3 from Arabidopsis. PLIP1 is a plastid phospholipase A1 that releases polyunsaturated fatty acids from chloroplast phosphatidylglycerol, leading to the export of the fatty acids to the ER for seed oil biosynthesis [
]. PLIP2/3 are also present in the chloroplasts. They respond to ABA and are involved in jasmonic acid biosynthesis [].
This is an N-terminal domain that is found adjacent to the patatin/phospholipase A2-related domain (see
) in a group of proteins. Proteins containing this domain include Tgl3/4/5 from Saccharomyces cerevisiae. Tgl3 is a bifunctional triacylglycerol lipase and lysophospholipid acyltransferase [
]. Tgl4/5 are multifunctional lipase/hydrolase/phospholipases [,
]. They are generally involved in triacylglycerol mobilisation and localized to lipid particles [,
].This entry also includes plant sugar-dependent 1 (SDP1) protein, which is a triacylglycerol lipase that initiates storage oil breakdown in germinating Arabidopsis seeds [
,
].
Diacylglycerol O-acyltransferase 1 (DGAT1) catalyses the final step in triacylglycerol synthesis by using diacylglycerol and fatty acyl CoA as substrates. In plants, diacylglycerol O-acyltransferase 1 (DGAT1, TAG1) is a major enzyme for oil accumulation in seeds. It has complementary functions with PDAT1 acyltransferase that are essential for triacylglycerol synthesis and normal development of both seeds and pollen [
,
,
,
,
].In mammals, DGAT1 is a multifunctional acyltransferase capable of synthesizing diacylglycerol, retinyl, and wax esters in addition to triacylglycerol [
]. In liver, it plays a role in esterifying exogenous fatty acids to glycerol []. It also functions as the major acyl-CoA retinol acyltransferase in the skin, where it acts to maintain retinoid homeostasis and prevent retinoid toxicity leading to skin and hair disorders [].
Plant seed storage proteins, whose principal function appears to be the major
nitrogen source for the developing plant, can be classified, on the basis oftheir structure, into different families. 11S-type globulins are non-glycosylated proteins which form hexameric structures [
,
]. Each of the subunits in the hexamer is itself composed of an acidic and a basic chain derived from a single precursor and linked by a disulphide bond. This structure is shown in the followingrepresentation.
+-------------------------+
| |xxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxxNGxCxxxxxxxxxxxxxxxxxxxxxxx
|------Acidic-subunit-------------||-----Basic-subunit------||-----------------About-480-to-500-residues-----------------|
'C': conserved cysteine involved in a disulphide bond.Members of the 11-S family include pea and broad bean legumins, oil seed rapecruciferin, rice glutelins, cotton beta-globulins, soybean glycinins, pumpkin
11-S globulin, oat globulin, sunflower helianthinin G3, etc.This family represents the precursor protein which is cleaved into
the two chains. These proteins contain two β-barrel domains.This family is a member of the 'cupin' superfamily on the
basis of their conserved barrel domain ('cupa' is the Latin termfor a small barrel).
Plant seed storage proteins, whose principal function appears to be the major
nitrogen source for the developing plant, can be classified, on the basis oftheir structure, into different families. 11-S are non-glycosylated proteins
which form hexameric structures [,
]. Each of the subunits in the hexamer isitself composed of an acidic and a basic chain derived from a single precursor
and linked by a disulphide bond. This structure is shown in the followingrepresentation.
+-------------------------+
| |xxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxxNGxCxxxxxxxxxxxxxxxxxxxxxxx
|------Acidic-subunit-------------||-----Basic-subunit------||-----------------About-480-to-500-residues-----------------|
'C': conserved cysteine involved in a disulphide bond.Members of the 11-S family include pea and broad bean legumins, oil seed rapecruciferin, rice glutelins, cotton beta-globulins, soybean glycinins, pumpkin
11-S globulin, oat globulin, sunflower helianthinin G3, etc.This family represents the precursor protein which is cleaved into
the two chains. These proteins contain two β-barrel domains.This family is a member of the 'cupin' superfamily on the
basis of their conserved barrel domain ('cupa' is the Latin termfor a small barrel).
The signature pattern for this family includes the conserved cleavage site between the acidic and basic subunits (Asn-Gly) and a proximal cysteine residue which is involved in the inter-chain disulphide bond.
