Heterodimer model

As shown in the bottom row of Fig. 18, the advantages of the dimer of dimers model over the heterodimer model are several (1) There is no need to disrupt the very stable SODl homodimer. (2) Instead of the 40-A movement by the CXC motif of domain 3 to the copper-binding site of SOD 1, the distance would be much shorter, minimizing the possibility of copper loss. The movement of copper from lower (MXCXXC) to higher (Cu,ZnSOD) affinity sites via domain 3 would occur in a very confined space and in a rapid time due to this proximity. (3) Copper can be delivered to both copper sites of dimeric SOD 1 simultaneously. (4) Practically... 

Two primary models have been used to describe tbe self-propagation of PrP-res. The heterodimer model (Griffith, 1967 Bolton and Bend-... 

Another factor besides PrP conformations in strain differences could be differences in PrP /PrP interaction surfaces, as with the models for species barriers discussed previously. For example, Warwicker (1997b) has interpreted his heterodimer model in light of residues important in determining strain differences. In particular, in this case, he focused on conserved and nonpolar residues and proposed that there are two distinct patches on the molecule that can interact with membrane or with a neighboring protein. This hypothesis leads to two different membrane-attached PrP orientations, or faces, that would be presented to an incoming PrP molecule. In a more recent study, Warwicker (1999) discusses how charge interactions between PrP and the membrane may affect scrapie formation. Along these lines, Morillas et al. 

Before considering the experimental ohservations relating to the mechanism of PrP-res formation, it may be helpful to have prevalent theoretical models of PrP-res formation in mind. A wide variety of mechanisms and permutations of mechanisms have been proposed for PrP-res formation. Two that are most commonly considered are the heterodimer model (Griffith, 1967 Bolton and Bendheim, 1988 Prusiner,... 

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