Molecular dynamics as a tool to detect protein foldability. A mutant of domain B1 of protein G with non-native secondary structure propensities

The usefulness of molecular dynamics to assess the structural integrity of mutants containing several mutations has been investigated. Our goal was to determine whether molecular dynamics would be able to discriminate mutants of a protein having a close-to-wild-type fold, from those that are not fol ded under the same conditions. We used as a model the B1 domain of protein G in which we replaced the unique central a-helix by the sequence of the se cond beta-hairpin, which has a strong intrinsic propensity to form this sec ondary structure in solution. In the resulting protein, one-third of the se condary structure has been replaced by a non-native one. Models of the muta nts were built based on the three-dimensional structure of the wild-type G( B1) domain. During 2 ns of molecular dynamics simulations on these models, mutants containing up to 10 mutations in the helix retained the native fold , while another mutant with an additional mutation unfolded. This result is in agreement with our circular dichroism and NMR experiments, which indica ted that the former mutants fold into a structure similar to the wild-type, as opposed to the latter mutant which is partly unfolded. Additionally, a mutant containing six mutations scattered through the surface of the domain , and which is unfolded, was also detected by the simulation. This study su ggests that molecular dynamics calculations could be performed on molecular models of mutants of a protein to evaluate their foldability, prior to a m utagenesis experiment.