Codon 129 polymorphism of the human prion protein influences the kinetics of amyloid formation. 
The human prion protein (PrP) has a common polymorphism at residue 129, which can be valine or methionine.  This polymorphism has a strong influence on susceptibility to prion diseases and on prion-strain properties.  Previous work has shown that this amino acid variation has no measurable effect on the native structure of cellular PrP (PrPC).  Here, it is shown that the polymorphism does not change the efficiency of conversion to the beta-PrP conformation or affect the binding of copper(II) ions.  However, in a partially denatured conformation, the polymorphic variation has a profound influence on the ability of the protein to form amyloid fibrils spontaneously.