  Here we propose that the upper bound marginal stability of proteins (7.4
kcal/mol) is a universal property that includes macro-molecular complexes and
is not affected by molecular changes such as mutations and Post-Translational
Modifications. Its existence is, essentially, a consequence of the Anfinsen
thermodynamic hypothesis rather than a result of an evolutive process. This
result enables us to conjecture that neutral evolution should also be, with
respect to protein stability, a universal phenomenon.
