Conformational calculations on the Ala14-Pro27 LCI segment of rabbit skeletal myosin

Abstract In order to define the conformational characteristics of a singular Ala 14 -Pro 27 segment in myosin LC1, conformational calculations were performed using the Simplex algorithm of Nelder and Mead (Computer J. 7 (1965) 308–313) in the ACME program proposed by Tournarie (J. Appl. Cryst. 6 (1973) 309–346). The (Ala-Pro) n = 1 unit was assigned a given conformation x; the conformation energy was then minimized for n = 1 to n = 7 by adjusting structural parameters (angle values). Similarly, 13 different possible conformations were optimized and compared, showing that a (β 2 R) 7 conformation is favored by about 20 kcal per mol over the next most probable conformation (C 7 R) 7 . In the β 2 R conformation, the (Ala-Pro) 7 segment is a wide helix, 15 A in length and 8.65 A in diameter, while the C 7 R conformation results in a semi-extended structure of 25 A long, with an approximate diameter of 6 A. These characteristics are in agreement with available experimental data and putative functions of the LC1 N-terminus.