Article

Fibril specific, conformation depended antibodies recognize a generic epitope common to amyloid fibrils and fibrillar oligomers that is absent in prefibrillar oligomers

Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA. .
Molecular Neurodegeneration (Impact Factor: 5.29). 02/2007; 2:18. DOI: 10.1186/1750-1326-2-18
Source: PubMed

ABSTRACT Amyloid-related degenerative diseases are associated with the accumulation of misfolded proteins as amyloid fibrils in tissue. In Alzheimer disease (AD), amyloid accumulates in several distinct types of insoluble plaque deposits, intracellular Abeta and as soluble oligomers and the relationships between these deposits and their pathological significance remains unclear. Conformation dependent antibodies have been reported that specifically recognize distinct assembly states of amyloids, including prefibrillar oligomers and fibrils.
We immunized rabbits with a morphologically homogeneous population of Abeta42 fibrils. The resulting immune serum (OC) specifically recognizes fibrils, but not random coil monomer or prefibrillar oligomers, indicating fibrils display a distinct conformation dependent epitope that is absent in prefibrillar oligomers. The fibril epitope is also displayed by fibrils of other types of amyloids, indicating that the epitope is a generic feature of the polypeptide backbone. The fibril specific antibody also recognizes 100,000 x G soluble fibrillar oligomers ranging in size from dimer to greater than 250 kDa on western blots. The fibrillar oligomers recognized by OC are immunologically distinct from prefibrillar oligomers recognized by A11, even though their sizes overlap broadly, indicating that size is not a reliable indicator of oligomer conformation. The immune response to prefibrillar oligomers and fibrils is not sequence specific and antisera of the same specificity are produced in response to immunization with islet amyloid polypeptide prefibrillar oligomer mimics and fibrils. The fibril specific antibodies stain all types of amyloid deposits in human AD brain. Diffuse amyloid deposits stain intensely with anti-fibril antibody although they are thioflavin S negative, suggesting that they are indeed fibrillar in conformation. OC also stains islet amyloid deposits in transgenic mouse models of type II diabetes, demonstrating its generic specificity for amyloid fibrils.
Since the fibril specific antibodies are conformation dependent, sequence-independent, and recognize epitopes that are distinct from those present in prefibrillar oligomers, they may have broad utility for detecting and characterizing the accumulation of amyloid fibrils and fibrillar type oligomers in degenerative diseases.

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    • "), confirming that in the context of reduced CIC levels, ATXN1 tends to form more organized fibrillar aggregates. We also probed FRA membranes with OC, a conformational antibody that specifically recognizes fibrillar oligomers and fibrils (Kayed et al., 2007), and found fractions 7 and 8 in Atxn1 154Q/+ mice, and fractions 7, 8, and 9 in Atxn1 154Q/+ ;Cic L+/-mice, positive for OC (Figure 4—figure supplement 3). ATXN1 thus tends to form fibrillar oligomers, amorphous aggregates and/or fibrils when CIC levels are reduced. "
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    • "folded monomers ( blue and red ) ( PDB entries 1BEG , 2LFM , 2GSP , and 2OTK ) . ( Georganopoulou et al . , 2005 ; Chikae et al . , 2008 ; Santos et al . , 2008 ; Herskovits et al . , 2013 ) . scrambled Aβ ( Walsh et al . , 2002 ) . There is plenty of direct exper - imental evidence to support the notion of toxic oligomers ( Walsh et al . , 2002 ; Kayed et al . , 2003 , 2007 ; Haass and Selkoe , 2007 ; Tomic et al . , 2009 ; Mucke and Selkoe , 2012 ; Lesne et al . , 2013 ) , also suggesting that the activity of causing dementia may occur across a broad oligomer range . For example , Aβ dodecamers were identified in human brain extracts and found to bind cul - tured neurons in a manner similar to synthetic A"
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    • "However, these transient structures and processes are difficult to probe in experiments (Bemporad & Chiti, 2012), and the molecular structure of the toxic amyloids and amyloid intermediates is therefore only poorly understood. Known is that they are unstable, rich in β-sheet structure, polymorphic and react with oligomer-recognizing antibodies , i.e., antibodies that bind only to the oligomers but not to fibrils (Benilova et al., 2012; Kayed et al., 2007; Lee, Culyba, Powers, & Kelly, 2011). There seems to be a correlation between toxicity and deviation from the energetically favorable and stable parallel in-register β-sheet amyloid state (Liu et al., 2012; Tycko & Wickner, 2013). "
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