Structure and Dynamics of Bacteriophage IKe Major Coat Protein in MPG Micelles by Solution NMR

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Abstract
The structure and dynamics of the 53-residue filamentous bacteriophage IKe major coat protein in fully protonated myristoyllysophosphatidylglycerol (MPG) micelles were characterized using multinuclear solution NMR spectroscopy. Detergent-solubilized coat protein (sequence: AEPNAATNYATEAMDSLKTQAIDLISQTWPVVTTVVVAGLVIRLFKKFSSKAV) mimics the membrane-bound “assembly intermediate” form of the coat protein which occurs during part of the phage life cycle. NMR studies of the IKe coat protein show that the coat protein is largely α-helical, exhibiting a long amphipathic surface helix (Asn 4 to Ser 26) and a shorter “micelle-spanning” C-terminal helix which begins at Trp 29 and continues at least to Phe 48. Pro 30 likely occurs in the first turn of the C-terminal helix, where it is ideally situated given the hydrogen bonding and steric restrictions imposed by this residue. The similarity of 15N relaxation values (T1, T2, and NOE at 500 MHz and T2 at 600 MHz) among much of the N-terminal helix and all of the TM helix indicates that the N-terminal helix is as closely associated with the micelle as the TM helix. The description of the protein in the micelle is supported by the observation of NOEs between lysolipid protons and protein amide protons between Asn 8 and Ser 50. The N-terminal and TM helices exhibit substantial mobility on the microsecond to second time scale, which likely reflects changes in the orientation between the two helices. The overall findings serve to clarify the role of individual residues in the context of a TM α-helix and provide an understanding of the secondary structure, dynamics, and aqueous and micellar environments of the coat protein.