> Having a protein with Known structure, have someone a general idea
> about how many aminoacids (percent) you can change without altering the
> protein structure? Do you have any reference about this problem?
> Thank you!
I recall a lecture about 10 years ago by somebody who tried to change
the specificity of amino-transferases. He changed a single amino acid in
the catalytic centre of the enzyme. The protein expressed fine but had
no enzyme activity left. After crystallization he found that the new
amino acid did not quite fit into the active site and hence had pushed a
beta-strand slightly out of its normal position. This minute change in
structure resulted in a non-functional protein.