Mouse Very-Low-Density-Lipoprotein Receptor (VLDLR) cDNA Cloning, Tissue-specific Expression and Evolutionary Relationship with the Low-density-lipoprotein Receptor

Authors


  • Note. The novel amino acid sequence data published here has been deposited with the Genebank sequence data bank and is available under accession number L33417.

  • Supplementary material. Mouse very-low-density-lipoprotein receptor (VLDLR) cDNA cloning, tissue-specific expression and evolutionary relationship with the low-density-lipoprotein receptor. Fig. S1. Alignment of amino acid sequence of mature VLDLR and LDLR proteins. This information is available, upon request, from the Editorial Office. A total of two pages are available.

  • Note added in the proof (received July 25, 1994). Since the submission of this manuscript, we became aware of a mouse VLDLR cDNA sequence submitted by Gafvels, M. E., Paavola, L. G., Boyd, C. O., Nolan, P. M., Wittmaack, F., Chawia, A., Lazar, M. Z., Bucan, M., Angelin, B. and Strauss, J. F. (1994) (GenBank accession No. U06670). The Gafvels sequence has 41 nucleotide differences and 16 deduced amino acid differences in the coding region of the cDNA compared to the sequence reported here. It also has a single nucleotide deletion and a duplication of a 17-nucleotide stretch in the 3′-untranslated region, whereas our sequence had only a single copy of this 17-nucleotide stretch. We have checked our sequence carefully and are confident that it is correct. The reason for the differences between the two sequences is unknown.

K. Oka, Department of Cell Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA

Abstract

The very-low-density-lipoprotein receptor (VLDLR) is a recently described lipoprotein receptor that shows considerable similarity to the low-density-lipoprotein receptor (LDLR). This receptor has been suggested to be important for the metabolism of apoprotein-E-containing triacylglycerol-rich lipoproteins, such as very-low-density-lipoprotein (VLDL), β-migrating VLDL and intermediate-density lipoprotein. cDNA clones that code for the VLDLR were isolated from a mouse heart cDNA library. The deduced amino acid sequence predicts a mature protein of 846 amino acids preceded by a 27-residue signal peptide. Three mRNA species for the VLDLR with sizes of 3.9, 4.5 and 7.9 kilobases were present in high concentration in heart and muscle, which utilize triacylglycerols as an energy source. VLDLR mRNA is also detected in decreasing amounts in kidney, brain, ovary, testis, lung and adipose tissue. It is essentially absent in liver and small intestine. The amino acid sequence of the VLDLR is highly conserved among rabbit, human and mouse. VLDLR contains five structural domains very similar to those in LDLR, except that the ligand-binding domain in VLDLR has an eightfold repeat instead of a sevenfold repeat in LDLR. Sequence conservation among animal species is much higher for the VLDLR than the LDLR. Sequences of the VLDLR from three vertebrate species and the LDLR from five vertebrate species were aligned and a phylogenetic tree was reconstructed. Although both receptors contain five domains and share amino acid sequence similarity, our computations showed that they diverged before the divergence between mammals and amphibians. In addition, sequence comparison of both receptor sequences suggests that the rabbit is evolutionarily closer to man than to the mouse. These results are consistent with the hypothesis that the VLDLR and the LDLR have evolved from a common ancestral gene to play distinct roles in lipoprotein metabolism and that the metabolic handling of triacylglycerol by the body via the VLDLR is a highly conserved mechanism.

Abbreviations
VLDLR

Very-low-density-lipoprotein receptor

LDLR

low-density-lipoprotein receptor

VLDL

very-low-density- lipoprotein

apo

apolipoprotein

IDL

intermediate-density lipoprotein

EGF

epidermal growth factor

Ancillary