Cross-seeding between the functional amyloidogenic CRES and CRES3 family members and their regulation of Aβ assembly

Hoa Quynh Do,Aveline Hewetson,Collin G Borcik,Mary Catherine Hastert,Sandra Whelly,Benjamin J Wylie,Roger Bryan Sutton,Gail A Cornwall

doi:10.1074/jbc.ra120.015307

Abstract

Accumulating evidence shows that amyloids perform biological roles. We previously showed that an amyloid matrix composed of four members of the CRES subgroup of reproductive family 2 cystatins is a normal component of the mouse epididymal lumen. The cellular mechanisms that control the assembly of these and other functional amyloid structures, however, remain unclear. We speculated that cross-seeding between CRES members could be a mechanism to control the assembly of the endogenous functional amyloid. Herein we used thioflavin T assays and negative stain transmission electron microscopy to explore this possibility. We show that CRES3 rapidly formed large networks of beaded chains that possessed the characteristic cross-β reflections of amyloid when examined by X-ray diffraction. The beaded amyloids accelerated the amyloidogenesis of CRES, a less amyloidogenic family member, in seeding assays during which beads transitioned into films and fibrils. Similarly, CRES seeds expedited CRES3 amyloidogenesis, although less efficiently than the CRES3 seeding of CRES. These studies suggest that CRES and CRES3 hetero-oligomerize and that CRES3 beaded amyloids may function as stable preassembled seeds. The CRES3 beaded amyloids also facilitated assembly of the unrelated amyloidogenic precursor Aβ by providing a surface for polymerization though, intriguingly, CRES3 (and CRES) monomer/early oligomer profoundly inhibited Aβ assembly. The cross-seeding between the CRES subgroup members is similar to that which occurs between bacterial curli proteins suggesting that it may be an evolutionarily conserved mechanism to control the assembly of some functional amyloids. Further, interactions between unrelated amyloidogenic precursors may also be a means to regulate functional amyloid assembly.

Highlights

Amyloids, defined as proteins that assemble into highly ordered cross β-sheet structures, have historically been considered as pathological assemblies that play causative roles in neurodegenerative diseases and prionopathies
Circular dichroism (CD) of the soluble fraction indicated a protein with mixed secondary structure that was predicted, based on the BestSel program that is optimized for β-sheet-rich proteins [24], to contain primarily antiparallel βsheets rather than the parallel β-sheets more commonly found in previously described amyloids (Fig. 1C)
This observation, was not unexpected based on prior CD, FTIR, X-ray crystallization, and NMR studies of the related CRES that revealed an antiparallel β-sheet-rich structure [25, 26]

Summary

Introduction

Amyloids, defined as proteins that assemble into highly ordered cross β-sheet structures, have historically been considered as pathological assemblies that play causative roles in neurodegenerative diseases and prionopathies. We performed cross-seeding experiments adding preformed CRES3 beaded chains to monomeric CRES and following amyloid assembly by thioflavin T (ThT) fluorescence and transmission electron microscopy (TEM).

Results

Conclusion