Mutations in the lower loop (L39-L42 and H40-H43) has already been found by Achim Knappik to have a profound effect on periplasmic production of antibody fragments in E.coli. Mutation of Pro H40 to Ala in mcpc (H11 construct) significantly reduced the toxicity of the antibody constructs. Constructs which show this toxicity lead to bacterial lysis as soon as production is induced. A similar effect was observed for the mutation of His H41 to Pro in antibody 4T5. The mutation does not significantly affect the thermodynamic stability of the scFV fragment. The effect is probably due to the interaction of soluble, misfolded species with components of the bacterial periplasm (disulfide bridge formation), since it is normally not seen in antibodies which are not produced in soluble form at all, increases as the folding behavior of these fragment is improved by mutations and disappears again in very efficient folders.

In abpc48, mutation of Asn H52 to Ser in CDR H2 has a marked effect on stability
Mutations in the "outer loop" have been shown to affect both stability and folding efficiency