The Golgi sialoglycoprotein MG160, expressed in Pichia pastoris, does not require complex carbohydrates and sialic acid for secretion and basic fibroblast growth factor binding

Abstract

MG160, a type I membrane sialoglycoprotein of the medial cisternae of the rat Golgi apparatus, shows high homology (over 90%) with CFR, a fibroblast growth factor receptor, and ESL-1, an E-selectin ligand of the cell surface of murine myeloid cells. When Chinese Hamster Ovary (CHO) cells were stably transfected with a cDNA lacking the transmembrane and C-terminus cytoplasmic domain of MG160 (ΔTMCT), a fully processed protein of 160 kDa apparent molecular mass was recovered in the culture medium. When these cells were treated with tunicymycin, a 130- to 140-kDa protein was immunoprecipitated from the culture medium. A construct lacking the signal sequence, the single transmembrane, and the cytoplasmic domains of MG160 (ΔTMCT-) was integrated at the HIS Pichia pastoris genome site using the expression vector pPIC 9 which possesses a yeast compatible signal sequence (Invitrogen). Recombinant protein accumulated in the medium to approximately 10 mg/L. The yeast recombinant protein lacked complex carbohydrates and sialic acid but bound 125I bFGF. Similarly, rat MG160 subjected to deglycosylation by peptide:N-glycosidase F (PNGase) bound 125I bFGF.