If its the same amino acid sequence then I would have thought it would fold in the same way. 😕

Insulin is like any other protein. This goes for all proteins: if the aminoacid sequence is the same, the protein will always fold the same way. we do not exactly how this works, how each protein knows exactly how to fold.. not yet. If there are errors in translation or transcription than the protein will not fold correctly.

The body has many ways to identify and get rid of these errors, which are quite common. An example that comes to my mind is the PEST sequence, which, if exposed, has a complementarity with lysosoms, and the protein will be hidrolysed

Yup…lysosoms are like supervisors in our body…little mistake and hydrolysed.. 😆
Just make it like this:
Example insulin protein have a chain: A-B-C-D-E (each of them is amino-acid)
To form that chain, our translation have to make the right amino-acids and bond it like the sequence above…(you can’t make insulin if the sequence is like..A-C-B-E-D)

Yeah protein folding is really a mystery! A unique sequence of amino acids determs how polypeptide chain folds and protein function. And don’t forget hydrogen bonds between hydrogen atom of amino group and oxygen atom of the carboxyl group in another part of the chain. Also don’t forget S-S bridges in insulin(S from cysteine). Most proteins can spontaneously fold(shape depends of hidrophility of each aminoacid)And for more complex proteins of course don’t forget chaperones-proteins that help other complex proteins to fold propperly. Mutation of some chaperons can be lethal-eg HSP90 .
Cheers!