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BIOMEDICINE: Moving the Goal Posts
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Stella M. Hurtley

The transmissible spongiform encephalopathies (TSEs), such as mad cow
disease and scrapie, are thought to be caused by aberrations in the
expression and conformation of the prion protein (PrP). Disease-inducing
forms of the PrP can be transferred from one animal host to another, but
the efficiency of disease transmission is affected by the characteristics
of the endogenous PrP in the recipient.
In examining the species barrier to transmission of three nonmurine TSEs,
Barron et al. discovered that a single amino acid change (from proline to
leucine at position 101) in mouse PrP produced a significant reduction in
the incubation period when these mice were challenged with inocula from
infected hamster and sheep. The same change, however, extended the
incubation time for susceptibility to a human source (a patient with
variant Creutzfeldt-Jakob disease) of infectivity. The authors speculate
that a structurally flexible region in PrP is particularly important in
maintaining the species barrier during TSE transmission. -- SMH
EMBO Journal 20, 5070 (2001).