Amyloid fibril formation by macrophage migration inhibitory factor

Abstract

We demonstrate herein that human macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine expressed in the brain and not previously considered to be amyloidogenic, forms amyloid fibrils similar to those derived from the disease associated amyloidogenic proteins b-amyloid and a-synuclein. Acid denaturing conditions were found to readily induce MIF to undergo amyloid fibril formation. MIF aggregates to form amyloid-like structures with a morphology that is highly dependent on pH. The mechanism of MIF amyloid formation was probed by electron microscopy, turbidity, Thioflavin T binding, circular dichroism spectroscopy, and analytical ultracentrifugation. The fibrillar structures formed by MIF bind Congo red and exhibit the characteristic green birefringence under polarized light. These results are consistent with the notion that amyloid fibril formation is not an exclusive property of a select group of amyloidogenic proteins, and contribute to a better understanding of the factors which govern protein conformational changes and amyloid fibril formation in vivo. Ó 2005 Elsevier Inc. All rights reserved.Keywords: Amyloid; Amyloid fibrils; AlzheimerÕs disease; Acid denaturation; Macrophage; Migration Inhibitory Factor; Cytokine; P53; Apoptosis; Sedimentation velocity; Electron microscopy Amyloidogenic proteins undergo a conformational change either prior to or coincident with their self-assembly into highly ordered fibrils that have a characteristic cross b-structure [1]. The presence of amyloid fibrils surrounding dead neurons in the brain is a hallmark of certain neurodegenerative conditions, including AlzheimerÕs disease, ParkinsonÕs disease, and Prion diseases. Amyloid formation in tissues can also be a pathological sequelae of many chronic inflammatory diseases [2,3]. Electron microscopic examination of the amyloid fibrils that form in vivo reveals long and unbranching filaments that are typically 10 nm in diameter. These fibrils often are detected in vivo by their ability to bind to the dye Congo red, which produces a characteristic green birefringence when illuminated by a polarized light source. Approximately 20 human proteins have been demonstrated to form amyloid in vivo, and several of these have been linked by genetic evidence with neurodegeneration and/or organ dysfunction [4]. A comparison of the primary sequence or tertiary structure of the 20 amyloidogenic proteins that occur in vivo has revealed no clear homology. Nevertheless, these amyloidogenic proteins are each capable of forming highly ordered fibrils of similar structure as discerned by X-ray fibril diffraction, electron, and atomic force microscopy [5]. The ability of these structurally and functionally diverse proteins to form amyloid fibrils with a common structure [6] is puzzling, and has been explained by the apparent tendency of these proteins to adopt a common, alternative b-sheet rich conformation (amyloidogenic intermediate(s)) that facilitates conversion into a cross-b amyloid structure 0006-291X/$ -see front ma...

The Conformational Flexibility of the Carboxy Terminal Residues 105−114 Is a Key Modulator of the Catalytic Activity and Stability of Macrophage Migration Inhibitory Factor

“…Using the partial specific volume calculated from the amino acid composition, we obtained molecular weights of 35.4 KDa, 35.9 KDa and 33.8 kDa for wt, ΔC5 huMIF 1-109 , and ΔC10 huMIF 1-104 respectively. Thus, our findings are fully consistent with a strongly associated trimeric quaternary structure of wt, as reported previously (36, 49), and mutants proteins. The slight decrease in the sedimentation coefficient values for the carboxy deleted proteins may reflect the small change in molecular weight and/or altered conformational properties of the mutants.…”

Formation of Amyloid-Like Fibrils by Y-Box Binding Protein 1 (YB-1) Is Mediated by Its Cold Shock Domain and Modulated by Disordered Terminal Domains

“…Noteworthily, the macrophage migration inhibitory factor secreted like YB-1 by a non-classical mechanism [52] can form amyloid-like fibrils. But these are effectively formed at pH <4, and their ability to dissociate in physiological conditions has not been assayed [53].…”

The Role of Macrophage Migration Inhibitory Factor in Alzheimer’s Disease

“…The recent report of a physical association and colocalization of MIF with the Aβ protein combined with the ability of MIF to form amyloid-like fibrils (17,28) suggests that MIF may play an important role in plaque formation and may be involved in the inflammatory process surrounding the plaques.…”