Table 3.

Interaction Energetics of Tropomyosin Segments Docked to F-Actin

Tpm segment	Interaction Energy Tpm for F-Actin C-State-Leaning Poses (kcal/mol)			Interaction Energy Tpm for F-Actin B-State-Facing Poses (kcal/mol)
	Electrostatic	van der Waals	Electrostatic + van der Waals	Electrostatic	van der Waals	Electrostatic + van der Waals
α2β2α3	−913	−22	−935	−1055	−11	−1066
α3β3α4	−1271	−31	−1302	−1175	−24	−1199
α4β4α5	−1219	−34	−1253	−1115	−17	−1132
α5β5α6	−1365	−58	−1423	−1086	−23	−1109
Overlap β6α7β7α1β1α2	−1132	−42	−1174	−1219	−36	−1255a
Total measured	−5900	−187	−6087	−5650	−111	−5761

Values for highest-ranked poses, i.e., in which the superhelical path of tropomyosin on F-actin target is followed. Please note that the interaction energy for pseudorepeats in the midpiece of tropomyosin is greater (more negative) for the C- versus the B-state tropomyosin, but values for the ends and the overlapping domain are the opposite, consistent with the possibility that the overlapping domain sets the initial twist of tropomyosin on actin and that TnI interactions might be important for establishing the B-state twist. In all cases, low-ranking poses representing tropomyosin delimited by the A-triad on actin (as in (14,48)) yielded poor (less negative) interaction energies (data not shown). Tabulation of values for α₁β₁α₂ and α₆β₆α₇ interactions is not measured because PIPER/ClusPro rigid-body docking protocols used do not allow for conformational twisting between α-zones at these sites and because their α₁ and α₇ are contained in overlapping structures on actin.

^aPositioning tropomyosin at the Li et al. azimuth (14) yields a 305 kcal/mol less negative value for the overlap-actin interaction.