Signal peptide design for improving recombinant protein secretion in the baculovirus expression vector system.

Almost all secretory proteins have a sequence consisting of 15-30 amino acids at the N-terminus (the so-called N-terminal signal peptide). Signal peptides direct the propeptide to the endoplasmic reticulum and through the secretory pathway. Although the sequences of signal peptides vary greatly, all contain a basic amino acid in the N-terminal region, followed by a hydrophobic core region. With the aim of improving the level of secretion of recombinant proteins in the baculovirus expression vector system (BEVS), we designed several signal peptides based on the signal peptide of silkworm SP1 by introducing the basic amino acid arginine into the N-terminal region and/or the polar amino acid asparagine into the C-terminal region of the silkworm SP1 signal peptide. Human interleukin (IL)-4, IL-13, and the extracellular domain of human IL-11 receptor alpha1 (IL-11Ralpha1) were fused to wild-type and modified SP1 signal peptides, and the effects that each signal peptide had on secretion were measured by enzyme-linked immunosorbent assay. Introduction of the basic amino acid arginine into the N-terminal region did not result in an increase in secretion of the recombinant proteins. On the other hand, introduction of the polar amino acid asparagine into the C-terminal region enhanced secretion of the recombinant proteins. Therefore, it is suggested that polar amino acids in the C-terminal region of signal peptides are important in the secretion of recombinant proteins in BEVS.