THE HSP150-DELTA-CARRIER CONFERS SECRETION COMPETENCE TO THE RAT NERVE GROWTH-FACTOR RECEPTOR ECTODOMAIN IN SACCHAROMYCES-CEREVISIAE

When the extracellular domain of rat low-affinity nerve growth factor receptor (NGFR(e)) was synthesized in Saccharomyces cerevisiae with th e signal peptide of invertase, NGFR(e) was translocated to the endopla smic reticulum (ER) and retained there. However, when NGFR(e) was fuse d to the C-terminus of the hsp150 Delta-carrier, the hsp150 Delta-NGFR (e) fusion protein was efficiently secreted to the growth medium with no apparent retention in the ER. The NGFR(e) portion was disulphide-bo nded and its single N-glycosylation site was occupied. The hsp150 Delt a-carrier is an N-terminal signal peptide-containing fragment of a yea st secretory glycoprotein. Hsp150 Delta-NGFR(e), harvested from the cu lture medium, inhibited the cross-linking of [I-125]NGF to authentic N GFR on the surface of human melanoma cells. Moreover, [I-125]NGF could be chemically cross-linked to secretory hsp150 Delta-NGFR(e), suggest ing that the NGFR(e) portion had adopted a ligand-binding conformation . However, inhibition of the cross-linking by unlabelled NGF was less effective than in the case of the authentic receptor. The hsp150 Delta -carrier may have potential in the production of mammalian proteins, w hich require elaborate folding and disulphide formation in the ER.