Amino acid sequence of the signal peptide of apoVLDL-II, a major apoprotein in avian very low density lipoproteins.

ApoVLDL-II is a major apoprotein in avian very low density lipoproteins (Jackson, R. L., Lin, H.-Y., Chan, L., and Means, A.R. (1977) J. Biol. Chem. 252, 250-253). Partially purified apoVLDL-II mRNA was translated in vitro in a wheat germ system in the presence of various labeled amino acids. The product, designated preapoVLDL-II, was purified by immunoprecipitation and sodium dodecyl sulfate acrylamide gel electrophoresis. It was subjected to automated Edman degradation in a Beckman Sequencer. The signal peptide was found to be a 23-amino acid NH2-terminal extension of the mature protein with the following sequence: Met-Gln-Tyr-Arg-Ala-Leu-Val-Ile-Ala-Val-Ile-Leu-Leu-Leu-Ser-Thr-Val-Pro-Glu-Val-Cys-Ser-Lys where Lys is the NH2-terminal residue of mature apoVLDL-II. The abundance and distribution of the hydrophobic amino acid residues are very similar to those of other signal sequences and the average hydrophobicity for the 23 residues is -1227 cal/mol/residue. However, translocation of preapoVLDL-II would represent a unique case of vectorial migration of a protein through a membrane since apoVLDL-II is itself an apolipoprotein and binds lipid spontaneously.