Conformational characterization of oligomeric intermediates and aggregatesin beta-lactoglobulin heat aggregation

In one of the first studies of isolated intermediates in protein aggregatio n, we have used circular dichroism and fluorescence spectroscopy to charact erize metastable oligomers that are formed in the early steps of beta -lact oglobulin heat aggregation. The intermediates show typical molten globule c haracteristics (secondary structure content similar to the native and less tight packing of the side chains), in agreement with the belief that partly folded states play a key role in protein aggregation. The far-UV CD signal bears strong resemblance to that of a known folding intermediate. Cryo-tra nsmission electron microscopy of the aggregates reveals spherical particles with a diameter of about 50 nm and an internal threadlike structure. Isola ted oligomers as well as larger aggregates bind the dye thioflavin T, usual ly a signature of the amyloid superstructures found in many protein aggrega tes. This result suggests that the structural motif recognized by thioflavi n T can be formed in small oligomers.