I am learning about proteins and we have learned that the C-N bond is rigid because of it's partial double-bond character. We have also learned that proline is commonly found in beta turns (type 1) because it can isomerize from trans to cis (which helps make the 180 degree turn).
I don't understand how these 2 things fit together--how can it change from trans to cis if it can't rotate around the C-N bond?
I found this which talks about the double bond being broken (in this case, it would be the partial double-bond, I guess) and then reforming...is that what is going on here?