Abstract
Assembly of an icosahedral capsid from a single species of coat protein subunit requires different subunit conformations at different lattice positions . In the double-stranded DNA bacteriophage P22 formation of correctly dimensioned capsids is mediated by interactions between subunits of coat and scaffolding proteins . We have employed Raman spectroscopy to investigate the specific intrasubunit conformations and intersubunit interactions required to close icosahedral shells which are competent to package the P22 genome . Preliminary results from coat protein subunits polymerized to form capsids in the presence and absence of the scaffolding protein indicate different distributions of subunit secondary structure for these two assembly conditions . The difference in structure affects a small portion of the coat subunit (z2 . 3 or 10 of 430 amino acid residues per subunit) and involves a transition from a-helix in the scaffoldassembled shell to B-strand in particles assembled without scaffold mediation . The secondary structure change is accompanied by changes in specific amino acid side chains indicative of a greater variety of side chain environments for particles assembled without scaffolding protein . The detection of small changes in protein structure is facilitated by recent developments in instrumentation and progress in the assignment of protein Raman bands to specific configurational states. Application of this methodology to the bacteriophage P22 tailspike protein has also permitted characterization of differences in thermal unfolding pathways of the wild-type protein and temperature-sensitive-folding mutant . Similar methods applied to mature icosahedral bacteriophages (P22 and TI) which package a double-stranded DNA chromosome reveal subtle but definitive perturbations to dsDNA conformation in the packaged state. 1.
Published Version
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