The PMCA Assay

This assay is based on the belief that the mis-folded PrP protein is the transmissible agent responsible for TSEs (SaborioNature 411:810,2001). Basically the mis-folded protein when incubated with normal protein catalyzes the mis-folding of other PrP proteins (i.e. hPrP^Sc converts rPrP^C rPrP^Sc as illustrated in the figure below). Normally this process occurs within cellular vesicles. The assay described above is however performed in a test tube (in vitro).

It should be noted that this conversion is very slow if pure hPrP^Sc and rPrP^C are mixed. A chaperone protein(s) appears to be necessary for efficient conversion (in the assay the test components are not purified rPrP^C and hPrP^Sc). The PrPs are from brain extracts. The extracts presumably contain the chaperone protein(s).

Not all of the rPrP^C is converted to rPrP^Sc in a single incubation, so the sample is incubated several times to get enough rPrP^C converted to rPrP^Sc to make detection easy (the numbers in the example above are meant only to illustrate how the test works not as absolute values). Once the incubations are complete the converted products are subjected to gel electrophoresis and the banding pattern is suggestive of presence and possibly the strain of TSE in the test sample.

This amplification of rPrP^C to rPrP^Sc in vitro: