A close-up view of the intersubunit cavity in the Na_VAb structure. Residues that show a prominent increase in mobility in Na_VSp1 in comparison to Na_VSp1-P are shown in red, and those that show a decrease in this parameter are represented in blue. The residues with higher mobility values are found to line the intersubunit cavity, which is at the interface of P1 and P2 helices from two adjacent subunits.