Nicotinic acetylcholine receptors (AChRs) isomerize (‘gate’) between a low affinity/non-conducting (R) and a high affinity/ion-conducting (R∗) conformation. Many different residues in this large, heteropentameric membrane protein have been shown to contribute to the free energy difference between the R and R∗ structures. Previously we showed that at the N-terminal ‘cap’ of the M2, pore-lining helix (positions 18′-27′) there are large and early energy changes in the α subunit whereas in the e subunit the residues are mostly iso-energetic. We measured the energy sensitivity (computed from the apparent range in diliganded equilibrium constant E2) and relative timing (Φ values) of the isomerization movements of residues in the N-terminal ‘cap’ domain of the δ and β subunits. We used cell attached, single-channel analysis to quantify the energetic consequences of point mutations (mouse α2βδe, HEK 293 cells, +70 mV pipette potential, cell-attached, 22° C , activated by 20 mM choline or 0.5 mM ACh). The probed positions were δ: I18′, S19′, K20′, R21′, L22′, P23′, A24′, T25′ and M27′ (a total of 43 mutants) and β:A19′, K21′, V22′, P23′, E24′, S26′, and L27′ (a total of 34 mutants). Of these, only one position, δS19′, showed a >2 kcal/mol range-energy (Φ = 0.20 ± 0.07). The only residues having a >10-fold range in E2 (1.35 kcal/mol) were: δ (18′, 19′, 20′, 21′ and 23′) and β (21′, 24′ and 27′). These all showed approximately the same Φ value: 0.30. Comparing this value to those in the ‘cap’ region of other subunits, the Φ-order is α > e > δ = β. The high Φ and large energy changes are apparently only in the α subunit M2-cap, which indicates that domain plays a special role in AChR gating. NIH (NS 23513, 064969)