title: Biosynthesis and secretion of insect lipoprotein: involvement of furin in cleavage of the apoB homolog, apolipophorin-II/I.
abstract: The biosynthesis of neutral fat-transporting lipoproteins involves the lipidation of their nonexchangeable apolipoprotein. In contrast to its mammalian homolog apolipoprotein B, however, insect apolipophorin-II/I (apoLp-II/I) is cleaved posttranslationally at a consensus substrate sequence for furin, resulting in the appearance of two apolipoproteins in insect lipoprotein. To characterize the cleavage process, a truncated cDNA encoding the N-terminal 38% of Locusta migratoria apoLp-II/I, including the cleavage site, was expressed in insect Sf9 cells. This resulted in the secretion of correctly processed apoLp-II and truncated apoLp-I. The cleavage could be impaired by the furin inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone (decRVKRcmk) as well as by mutagenesis of the consensus substrate sequence for furin, as indicated by the secretion of uncleaved apoLp-II/I-38. Treatment of L. migratoria fat body, the physiological site of lipoprotein biosynthesis, with decRVKRcmk similarly resulted in the secretion of uncleaved apoLp-II/I, which was integrated in lipoprotein particles of buoyant density identical to wild-type high density lipophorin (HDLp). These results show that apoLp-II/I is posttranslationally cleaved by an insect furin and that biosynthesis and secretion of HDLp can occur independent of this processing step. Structure modeling indicates that the cleavage of apoLp-II/I represents a molecular adaptation in homologous apolipoprotein structures. We propose that cleavage enables specific features of insect lipoproteins, such as low density lipoprotein formation, endocytic recycling, and involvement in coagulation.
authors.affiliation: Department of Biochemical Physiology, Faculty of Biology, Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands.
authors.forename: Marcel M W
authors.initials: MM
authors.lastname: Smolenaars
authors.forename: Marcelle A M
authors.initials: MA
authors.lastname: Kasperaitis
authors.forename: Paul E
authors.initials: PE
authors.lastname: Richardson
authors.forename: Kees W
authors.initials: KW
authors.lastname: Rodenburg
authors.forename: Dick J
authors.initials: DJ
authors.lastname: Van der Horst
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D001053:Apolipoproteins / Q000096:biosynthesis / Q000378:metabolism*; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D045683:Furin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048188:Locusta migratoria / Q000201:enzymology; D043484:Proprotein Convertases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D001053:Apolipoproteins; D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; C042470:apolipophorin III; D043484:Proprotein Convertases; D045683:Furin