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Papers In Press, published online ahead of print December 16, 2004
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Biochemical Physiology, Faculty of Biology, and Institute of Biomembranes, Utrecht University, Utrecht 3584 CH
Corresponding Author: m.m.w.smolenaars{at}bio.uu.nl
The biosynthesis of neutral fat-transporting lipoproteins involves the lipidation of their non-exchangeable apolipoprotein. In contrast to its mammalian homologue apolipoprotein B, however, insect apolipophorin-II/I (apoLp-II/I) is cleaved post-translationally 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 decRVKRcmk as well as mutagenesis of the consensus substrate sequence for furin, as evidenced 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, that was integrated in lipoprotein particles of buoyant density identical to wild-type high-density lipophorin (HDLp). These results show that apoLp-II/I is post-translationally 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, or involvement in coagulation.
Revised on November 24, 2004
Accepted on December 9, 2004
Biosynthesis and secretion of insect lipoprotein: involvement of furin in cleavage of the insect apolipoprotein B homologue, apolipophorin-II/I
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