These fibrils then congeal into tangled plaques. For the past few years, scientists in the field have been focusing considerable efforts on developing molecules that would inhibit A aggregation or perhaps even break up existing plaques. In this quest, they have recently turned their attention to antibodies that bind to different portions of the A peptide.
In their study, Kowalewski and a graduate student, Justin Legleiter, incubated the A peptide in solution with two different monoclonal antibodies: m3D6, which binds near one end of the peptide called the amino terminus, and m266.2, which binds to the peptide's central portion.
Over several days, the researchers placed drops of the sample solutions on mica sheets and observed the degree of protein aggregation using AFM. The m266.2 antibody proved much better than m3D6 at preventing the formation of amyloid fibrils.
"Interestingly, we found that both antibodies interfere with the formation of protofibrils, or fibril precursors," noted Kowalewski. "In solutions of A alone, numerous protofibrils were present under our experimental conditions as early as the third day, whereas in the presence of m3D6 they grew at a slower rate. We found that m266.2 completely inhibited protofibril formation."
The scientists believe that the two antibodies differ in their ability to inhibit fibril formation due to the way they bind to the A peptide. Binding at one end of A, m3D6 does not inhibit the formation of extended beta sheets, which are the major structural feature of mature fibrils. Because m266.2 binds to the center of A, it blocks the formation of these extended beta sheets, the investigators surmised.
In AFM, a tiny lever ending with an ultra-sharp tip is scanned across a surface from side-to-side and top-to-bottom, much as a cursor moves across a computer screen. A lase
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Contact: Lauren Ward
wardle@andrew.cmu.edu
412-268-7761
Carnegie Mellon University
20-Jan-2004