Lipophorin
Lipophorin is a lipid-carrying protein of insects, first identified in 1981,[1] and is the major lipoprotein in the plasma of insects. Lipophorin has been identified in all insect species, in every life stage. Recently, additional nomenclature has been introduced to designate specific lipophorin subspecies that differ in lipid and/or apoprotein content. The concentration of lipophorin subspecies (HDLp and LDLp) changes can be considered to reflect the physiological state of the organism with respect to lipid metabolism.[2] The versatility of this particle concerning its lipid binding capacity may be unparalleled in nature.
Biosynthesis
[edit]Lipophorins are synthesized in fat body and secreted into hemolymph. In larval Manduca sexta, nascent lipophorin particles were synthesized from fat body cells and they associate with phospholipid to form a nascent Very High Density Lipophorin (VHDLp), which is essentially devoid of diacylglycerol. The VHDLp is then secreted into the hemolymph, where it later interacts with the mid gut to load DAG, which is derived from dietary lipids.[3] The maturation of lipophorin into circulating High Density Lipophorin (HDLp) results in a density shift from 1.26 to 1.15 g/ml with no change in apoprotein content. The lipophorin contains two structural apolipoproteins, derived from ApoLp-II/I precursor by enzymatic cleavage (furin).[4] Furin is a member of the proprotein convertase family of subtilisin like serine endoproteases that is mainly active in the trans-Golgi network.[5] The favored consensus substrate sequence for furin, R-X-K/R-R, is present in all precursor sequences characterized to date.[6] In agreement with the activity of furin, Locusta migratoria ApoLp II/I precursor appears to be cleaved C-terminal of its furin substrate sequence, RQKR, as indicated by the N-terminal sequence of ApoLp I.[7]
Structure
[edit] |
Lipophorins are large, amphipathic complexes composed of proteins and lipids. They are structurally similar to vertebrate lipoproteins, like low-density lipoproteins (LDL) and high-density lipoproteins (HDL). The core of a lipophorin particle typically consists of nonpolar lipids, such as diacylglycerols and hydrocarbons, surrounded by a layer of phospholipids, cholesterol, and apolipoproteins.
Two primary proteins are associated with lipophorins:
Apolipophorin-I (ApoLp-I): The major structural protein that provides stability to the particle.
Apolipophorin-II (ApoLp-II): A smaller protein that functions in lipid binding and transport.
Types of Lipophorins
[edit]Lipophorins are generally classified based on their density and function:
High-Density Lipophorin (HDLp): A lipid-poor version, primarily used for initial lipid transport in the hemolymph.
Low-Density Lipophorin (LDLp): A lipid-enriched form that is generated when lipophorins acquire lipids, such as diacylglycerol, from tissues.
References
[edit]- ^ Chino, H.; Downer, R. G. H.; Wyatt, G. R.; Gilbert, L. I. (1 January 1981). "Lipophorins, a major class of lipoproteins of insect haemolymph". Insect Biochemistry. 11 (4): 491. doi:10.1016/0020-1790(81)90085-8.
- ^ PRATHEEP, Thangaraj; RAMESHKUMAR, Neelamegam; KAYALVIZHI, Nagarajan; SUGANYA, Thangaiyan; KARTHIKEYAN, Sivashanmugam; KRISHNAN, Muthukalingan (2017). "Changes in lipophorin composition during late larval, pupal and adult stages of Bombyx mori". Acta Entomologica Sinica. 60 (3): 247-253. doi:10.16380/j.kcxb.2017.03.002.
- ^ Prasad, S V; Ryan, R O; Law, J H; Wells, M A (15 January 1986). "Changes in lipoprotein composition during larval-pupal metamorphosis of an insect, Manduca sexta". Journal of Biological Chemistry. 261 (2): 558–562. doi:10.1016/S0021-9258(17)36128-8. ISSN 0021-9258. PMID 3941091.
- ^ Van der Horst, Dick J.; Van Hoof, Dennis; Van Marrewijk, Wil J.A.; Rodenburg, Kees W. (1 October 2002). "Alternative lipid mobilization: The insect shuttle system". Molecular and Cellular Biochemistry. 239 (1): 113–119. doi:10.1023/A:1020541010547.
- ^ Taylor, Neil A.; Van De Ven, Wim J. M.; Creemers, John W. M. (2003). "Curbing activation: proprotein convertases in homeostasis and pathology". The FASEB Journal. 17 (10): 1215–1227. doi:10.1096/fj.02-0831rev. ISSN 1530-6860.
- ^ Kutty, R. Krishnan; Kutty, Geetha; Kambadur, Ravi; Duncan, Todd; Koonin, Eugene V.; Rodriguez, Ignacio R.; Odenwald, Ward F.; Wiggert, Barbara (23 August 1996). "Molecular Characterization and Developmental Expression of a Retinoid- and Fatty Acid-binding Glycoprotein from Drosophila: A PUTATIVE LIPOPHORIN *". Journal of Biological Chemistry. 271 (34): 20641–20649. doi:10.1074/jbc.271.34.20641.
- ^ Bogerd, Jan; Babin, Patrick J.; Kooiman, Frank P.; André, Michele; Ballagny, Chantal; Van Marrewijk, Wil J.A.; Van Der Horst, Dick J. (2000). "Molecular characterization and gene expression in the eye of the apolipophorin II/I precursor from Locusta migratoria". Journal of Comparative Neurology. 427 (4): 546–558. doi:10.1002/1096-9861(20001127)427:4<546::AID-CNE4>3.0.CO;2-H. PMID 11056463.
.svg){kind=small} | This biochemistry article is a stub. You can help Wikipedia by expanding it. |