Isolation, primary structures and metal binding properties of neuronal growth inhibitory factor (GIF) from bovine and equine brain

Abstract

Human neuronal growth inhibitory factor (GIF) impairs the survival of cultured neurons and is deficient in the brains of Alzheimer's disease victims. We have isolated and sequenced analogous proteins from bovine and equine brain. By comparing their primary structures with those of human, mouse and rat GIFs, a consensus GIF sequence was obtained. Although this exhibits ca. 65% similarity with primary structures of mammalian metallothioneins (MTs), some significant differences are expected in the content of helix and turn secondary structures. In contrast to MTs, which usually bind 7 Zn(II) ions, human, bovine and equine GIFs contain 1–4 Cu(I) and 3–5 Zn(II) ions in species-specific ratios. The observed Cu(I) phosphorescence (λ_max 550–590 nm; τ, 100 μs at 77 K) indicates the presence of the cuprous ion. Both bovine Cu₁Cd₅- and the equine Cu₃Cd₃-GIF derivatives (Cd replacing Zn) exhibit cadmium-dependent absorption and CD features between 220–260 nm characteristic of Cd-thiolate clusters similar to those in Cd-MTs.