POSTERS - BLAST X - University of Utah

BLAST X Thurs. Morning Session
PROTEIN MISFOLDING DONE RIGHT: THE BIOGENESIS OF BACTERIAL AMYLOID
FIBERS
Xuan Wang, Neal Hammer and Matt Chapman
University of Michigan, Department of Molecular, Cellular and Developmental Biology, Ann
Arbor, MI, 48109
Many Enterobacteriaceae spp., including E. coli, produce surface-localized amyloid
fibers called curli. Curli fibers are associated with biofilm formation, host cell adhesion and
invasion, and immune system activation. Unlike disease-associated amyloid formation, curli
biogenesis is a directed and highly regulated process. The major curli subunit protein, CsgA,
polymerizes into amyloid after interacting the CsgB nucleator protein. CsgB presents an
amyloid-like template to CsgA on the cell surface that initiates fiber formation. CsgA has five
imperfect repeating units (R1-R5) that are each predicted to form strand-loop-strand structures.
Asn and Gln residues in R1 and R5 were found to be required for efficient amyloid formation
and for interaction with the CsgB nucleator protein. Furthermore, the polymerization of CsgA
was tempered by the presence of conserved aspartic residues in R2, R3 and R4. When these
aspartic acid residues were changed to alanine (CsgA*), polymerization was significantly faster
in vitro. Even more remarkable was the observation that CsgA* assembled into an amyloid fiber
in vivo in the absence of CsgB. The ability of CsgA* to polymerize into amyloid more efficiently,
and in the absence of CsgB, was not without consequences. Cells expressing CsgA* grew more
slowly when compared to cells expressing wild type CsgA. This analysis suggests that aspartic
acid residues can potently inhibit functional amyloid formation. CsgA has apparently evolved to
efficiently assemble into an amyloid in vivo only in the presence of CsgB. This suggests an
elegant mechanism to control amyloid formation by regulating the temporal and spatial
interactions between CsgA and CsgB.
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