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Journal of Lipid Research, Vol. 48, 1955-1965, September 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology

Insect lipoprotein biogenesis depends on an amphipathic ß cluster in apolipophorin II/I and is stimulated by microsomal triglyceride transfer protein

Marcel M. W. Smolenaars, Antoine de Morrée, Jana Kerver, Dick J. Van der Horst and Kees W. Rodenburg¹

Division of Endocrinology and Metabolism, Department of Biology and Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands

Published, JLR Papers in Press, June 13, 2007.

¹ To whom correspondence should be addressed. e-mail: c.w.rodenburg{at}uu.nl

Lipoproteins transport lipids in the circulation of an evolutionally wide diversity of animals. The pathway for lipoprotein biogenesis has been revealed to a large extent in mammals only, in which apolipoprotein B (apoB) acquires lipids via the assistance of microsomal triglyceride transfer protein (MTP) and binds them by means of amphipathic protein structures. To investigate whether this is a common mechanism for lipoprotein biogenesis in animals, we studied the structural elements involved in the assembly of the insect lipoprotein, lipophorin. LOCATE sequence analysis predicted that the insect lipoprotein precursor, apolipophorin II/I (apoLp-II/I), contains clusters of amphipathic -helices and ß-strands, organized along the protein as N-₁-ß-₂-C, reminiscent of a truncated form of apoB. Recombinant expression of a series of C-terminal truncation variants of Locusta migratoria apoLp-II/I in an insect cell (Sf9) expression system revealed that the formation of a buoyant high density lipoprotein requires the amphipathic ß cluster. Coexpression of apoLp-II/I with the MTP homolog of Drosophila melanogaster affected insect lipoprotein biogenesis quantitatively as well as qualitatively, as the secretion of apoLp-II/I proteins was increased several-fold and the buoyant density of the secreted lipoprotein decreased concomitantly, indicative of augmented lipidation. Based on these findings, we propose that, despite specific modifications, the assembly of lipoproteins involves MTP as well as amphipathic structures in the apolipoprotein carrier, both in mammals and insects. Thus, lipoprotein biogenesis in animals appears to rely on structural elements that are of early metazoan origin.

Supplementary key words evolution • metabolism • Locusta migratoria • Drosophila melanogaster • Sf9 cells • lipid droplet • large lipid transfer protein • apolipoprotein • lipophorin • apolipoprotein B

Abbreviations: aa, amino acids; apoB, apolipoprotein B; apoLp-II/I, apolipophorin II/I; dMTP, Drosophila melanogaster microsomal triglyceride transfer protein; HDLp, high density lipophorin; LLT, large lipid transfer; MTP, microsomal triglyceride transfer protein; vWF, von Willebrand Factor

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