Overexpression of juvenile hormone binding protein in bacteria and Pichia pastoris

N-linked glycosylation of G. mellonella juvenile hormone binding protein - comparison of recombinant mutants expressed in P. pastoris cells with native protein

Juvenile hormone (JH) regulates insect growth and development. JH present in the hemolymph is bound to juvenile hormone binding protein (hJHBP) which protects JH from degradation. In G. mellonella, this protein is glycosylated only at one (Asn(94)) of the two potential N-linked glycosylation sites (Asn(4) and Asn(94)). To investigate the function of glycosylation, each of the two potential glycosylation sites in the rJHBP molecule was examined by site-directed mutagenesis. MS analysis revealed that rJHBP overexpressed in the P. pastoris system may appear in a non-glycosylated as well as in a glycosylated form at both sites. We found that mutation at position Asn(94) reduces the level of protein secretion whereas mutation at the Asn(4) site has no effect on protein secretion. Purified rJHBP and its mutated forms (N4W and N94A) have the same JH binding activities similar to that of hJHBP. However, both mutants devoid of the carbohydrate chain are more susceptible to thermal inactivation. It is concluded that glycosylation of JHBP molecule is important for its thermal stability and secretion although it is not required for JH binding activity.

Immunosensor incorporating anti-His (C-term) IgG F(ab') fragments attached to gold nanorods for detection of His-tagged proteins in culture medium

Immunosensors based on gold electrodes (electrochemical) or gold discs (optical) modified with 1,6-hexanedithiol, gold nanorods and Anti-His (C-term) monoclonal antibody F(ab’) fragment are described. The antigen detected by the sensing platform is a recombinant histidine-tagged silk proteinase inhibitor (rSPI2-His₆). Electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) techniques were used as methods for detection of the antigen. This approach allows to detect the antigen protein in concentration of 10 pg per mL (0.13 pM) of culture medium. The immunosensor shows good reproducibility due to covalent immobilization of F(ab’) fragments to gold nanorods layer.

Structurally unique recombinant Kazal-type proteinase inhibitor retains activity when terminally extended and glycosylated

Recombinant derivatives of the Kazal-type serine proteinase inhibitor GmSPI2 (36 amino acid residues), which is a component of insect silk, were prepared in the expression vector Pichia pastoris. The rhSPI2 had a C-terminal hexahistidine tag attached to the GmSPI2 sequence, rtSPI2 was extended with GluAlaAla at the N-terminus, and rfSPI2 included this N-terminal extension and a C-terminal tail of 22 residues (myc epitope and hexahistidine). A portion of the secreted rfSI2 was O-glycosylated with a trimannosyl or hexamannosyl. The native inhibitor was active slightly on trypsin and highly on subtilisin and proteinase K. The extended C-terminus in rhSPI2 and rfSPI2 enhanced activity on the two latter enzymes and rendered rfSPI2 active on elastase and pronase, but abolished the inhibition of trypsin. The glycosylation of rfSPI2 reduced its inhibitory activity to a level comparable with the native inhibitor. The rtSPI2 with tripeptide extension at the N-terminus and no C-terminal modification was clearly less active than the native inhibitor. None of the tested compounds inhibited alpha-chymotrypsin and the non-serine proteinases.

Positions of disulfide bonds and N-glycosylation site in juvenile hormone binding protein

The juvenile hormone binding protein (JHBP) from Galleria mellonella hemolymph is a glycoprotein composed of 225 amino acid residues. It contains four Cys residues forming two disulfide bridges. In this study, the topography of the disulfide bonds as well as the site of glycan attachment in the JHBP molecule from G. mellonella was determined, using electrospray mass spectrometry. The MS analysis was performed on tryptic digests of JHBP. Our results show that the disulfide bridges link Cys10 and Cys17, and Cys151 and Cys195. Of the two potential N-glycosylation sites in JHBP, Asn4, and Asn94, only Asn94 is glycosylated. This site of glycosylation is also found in the fully biologically active recombinant JHBP expressed in the yeast Pichia pastoris.