  The second domain of gelsolin (G2) hosts mutations responsible for a
hereditary form of amyloidosis. The active form of gelsolin is Ca2+-bound; it
is also a dynamic protein, hence structural biologists often rely on the study
of the isolated G2. However, the wild type G2 structure that have been used so
far in comparative studies is bound to a crystallographic Cd2+, in lieu of the
physiological calcium. Here, we report the wild type structure of G2 in complex
with Ca2+ highlighting subtle ion-dependent differences. Previous findings on
different G2 mutations are also briefly revised in light of these results.
