STRUCTURE AND DYNAMICS OF BACTERIOPHAGE-IKE MAJOR COAT PROTEIN IN MPGMICELLES BY SOLUTION NMR

The structure and dynamics of the 53-residue filamentous bacteriophage IKe major coat protein in fully protonated myristoyllysophosphatidylg lycerol (MPG) micelles were characterized using multinuclear solution MMR spectroscopy. Detergent-solubilized coat protein (sequence: AATNYA TEAMDSLKTQAIDLISQTWPVVTTVVVAGLVIRLFKKFSSKAV) mimics the membrane-bound ''assembly intermediate'' form of the coat protein which occurs durin g part of the phage Life cycle. NMR studies of the IKe coat protein sh ow that the coat protein is largely alpha-helical, exhibiting a long a mphipathic surface helix (Asn 4 to Ser 26) and a shorter ''micelle-spa nning'' 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 h elix, where it is ideally situated given the hydrogen bonding and ster ic restrictions imposed by this residue. The similarity of N-15 relaxa tion values (T-1, T-2, and NOE at 500 MHz and T-2 at 600 MHz) among mu ch 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 h elix. The description of the protein in the micelle is supported by th e observation of NOEs between lysolipid protons and protein amide prot ons between Asn 8 and Ser 50. The N-terminal and TM helices exhibit su bstantial mobility on the microsecond to second time scale, which Like ly reflects changes in the orientation between the two helices. The ov erall findings serve to clarify the role of individual residues in the context of a TM alpha-helix and provide an understanding of the secon dary structure, dynamics, and aqueous and micellar environments of the coat protein.