Design and structural analysis of a thermostable nine-beta-stranded immunoglobulin scaffold.

A small and stable protein scaffold, consisting of nine beta-strands and able to functionally present affinity peptide loops, was designed. Computational methods were used to predict sequences with low free energy derived from a naturally occurring single-chain camel antibody. Genes for two redesigned proteins (with respectively 88% and 76% identity with the original sequence) were synthesized and the proteins were expressed, purified, and subsequently characterized using circular dichroism (CD) and NMR experiments. The redesigned proteins appear to be monomeric and demonstrate CD and NMR spectra similar to the wild type, which is consistent with a well-packed immunoglobulin structure. These encouraging results indicate that the computational protein design method can identify amino acid sequences compatible with an immunoglobulin fold