All-or-none N-glycosylation in primate follicle-stimulating hormone beta-subunits

Abstract

Human FSH exists as two major glycoforms designated, tetra-glycosylated and di-glycosylated hFSH. The former possesses both alpha- and beta-subunit carbohydrates while the latter possesses only alpha-subunit carbohydrate. Western blotting differentiated the glycosylated, 24,000 M(r) hFSHbeta band from the non-glycosylated 21,000 M(r) FSHbeta band. Postmenopausal urinary hFSH preparations possessed 75-95% 24,000 M(r) hFSHbeta, while pituitary hFSH immunopurified from 21- to 43-year-old females and 21-43-year-old males possessed only 35-40% 24,000 M(r) hFSHbeta. The pituitary hFSH from a postmenopausal woman on estrogen replacement was 75% 21,000 M(r) hFSHbeta. Other immunopurified postmenopausal pituitary hFSH preparations possessed 50-60% 21,000 M(r) hFSHbeta. Gel filtration removed predominantly 21,000 M(r) free hFSHbeta and reduced its abundance to 13-22% in postmenopausal pituitary hFSH heterodimer preparations. A major regulatory mechanism for FSH glycosylation involves control of beta-subunit N-glycosylation, possibly by inhibition of oligosaccharyl transferase. Two primate species exhibited the same all-or-none pattern of pituitary FSHbeta glycosylation.