| ENERGY MINIMIZATION WITH ORIENTATIONAL CONSTRAINTS |
REFINEMENT WAS CARRIED OUT IN VACUO ON INITIAL MONOMER COORDINATES CONSISTING OF TWO ALPHA-HELICAL FRAGMENTS (3.6 RESIDUES PER TURN) HAVING TILT AND ROTATIONAL ORIENTATIONS WITH RESPECT TO THE BILAYER DERIVED FROM PISEMA DIPOLAR WAVE ANALYSIS. ENERGY MINIMIZATION USED A GLOBAL PENALTY FUNCTION INCORPORATING ORIENTATIONAL RESTRAINTS, HYDROGEN BONDING AND THE CHARMM EMPIRICAL FUNCTION. THE ORIENTATIONAL RESTRAINTS IMPOSED ON THE STRUCTURE DURING REFINEMENT ARE 16 15N CHEMICAL SHIFTS AND 16 15N-1H DIPOLAR COUPLINGS FROM PISEMA EXPERIMENTS. A SYMMETRIC, TETRAMERIC BUNDLE MODEL OF M2-TMD WAS CONSTRUCTED BY A SERIES OF RIGID-BODY TRANSFORMATIONS OF THE REFINED M2-TMD MONOMER. THE RESULTING HOMO-TETRAMER IS THE LOWEST FREE ENERGY CONFORMER BASED ON ROTATIONAL CONFORMATIONAL SEARCH. NOTE THAT THE HIS37 AND TRP41 SIDECHAIN POSITIONS ARE CONSISTENT WITH MEASURED ORIENTATIONAL CONSTRAINTS. THE ROTAMERIC STATES OF OTHER RESIDUES ARE TAKEN FROM A BACKBONE DEPENDENT SIDECHAIN ROTAMER LIBRARY (SCRWL). |
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