Conversion of monomeric protein L to an obligate dimer by computational protein design

Protein L consists of a single a-helix packed on a four-stranded beta -shee t formed by two symmetrically opposed beta -hairpins. We use a computer-bas ed protein design procedure to stabilize a domain-swapped dimer of protein L in which the second beta -turn straightens and the C-terminal strand inse rts into the beta -sheet of the partner. The designed obligate dimer contai ns three mutations (A52V, N53P, and G55A) and has a dissociation constant o f approximate to 700 pM, which is comparable to the dissociation constant o f many naturally occurring protein dimers. The structure of the dimer has b een determined by x-ray crystallography and is close to the in silico model .