Protein sequence diversity

The repeat gene family tandem repeats may increase both intra- and intermolecular recombination events, which result in gene or epitope amplification that is usually followed by sequence divergence. This could be another strategy of adaptation by the virus to keep pace with its evolving host. Because of its potentially large size and sequence diversity, the 540-bp repeat gene family will presumably play an important role. Based upon predicted properties, the 540-bp repeat proteins are believed to function differently than those of the cysteine-rich family. 

Amyloid fibrils form from a variety of native proteins with diverse sequences and folds. The classic method for the structural analysis of amyloid has been X-ray fiber diffraction amyloid fibrils exhibit a characteristic diffraction signature, called the cross-/) pattern. This cross-/ pattern suggested a repeating structure in which /1-sheets run parallel to the fiber axis with their constituent /1-strands perpendicular to that direction (Sunde and Blake, 1997). This diffraction signature pointed to an underlying common core molecular structure for the amyloid fibril that could accommodate diverse sequences and folds. A number of groups have proposed amyloid folds that are consistent with the experimental data and these can be linked to repeating /1-structured units. 

As discussed for N-myristoylation and S-prenylation, even S-acylation of proteins with a fatty acid which in the vast majority of cases is the C16 0 palmitic acid, plays a fundamental role in the cellular signal-transduction process (Table l). 2-5 14 While N-myristoylation and S-prenylation are permanent protein modifications due to the amide- and sulfide-type linkage, the thioester bond between palmitic acid and the peptide chain is rather labile and palmi-toylation is referred to as a dynamic modification. 64 This reversibility plays a crucial role in the modulation of protein functions since the presence or absence of a palmitoyl chain can determine the membrane localization of the protein and can also be used to regulate the interactions of these proteins with other proteins. Furthermore, a unique consensus sequence for protein palmitoylation has not been found, in contrast to the strict consensus sequences required for N-myristoylation and S-prenylation. Palmitoylation can occur at N- or C-terminal parts of the polypeptide chain depending on the protein family and often coexists with other types of lipidation (see Section 6.4.1.4). Given the diversity of protein sequences... 

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