STRUCTURAL BIOLOGY OF MACROMOLECULAR STRUCTURE

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This Laboratory seeks to elucidate the mechanisms that govern the assembly of supramolecular complexes and the folding of macromolecules, as well as those that underlie the synthesis of viruses, organelles, and other high order structures. In the past year, we have discovered a radical departure from equivalence in the packing of protein molecules in the capsid of bacteriophage HK97. The same protein forms both the hexons and pentons, but whereas the pentons are cyclically symmetric pentamers, the hexons are not cyclically symmetric, but consist of two apposed trimers with a mutual lateral displacement of at least 20 Angstroms. In herpes simplex virus, we have localized the small abundant capsid protein, VP26 (12 Kda) to the outer tips of hexons by quantitative difference imaging. Its exposed location suggests that its role may lie in coupling the capsid to the surrounding tegument. We have also studied several of the major molecules displayed at the outer surface of the pathogenic bacterium, Bordetella pertussis. One of these, filamentous hemagglutinin, is a high immunogenic adhesion. FHA was found to assume a novel 50nm-long monomeric hairpin structure. Its sequence contains two protracted runs of 19-residue repeats which strongly resemble the leucine-rich repeats (LRRs) that are present in a set of eukaryotic proteins, many of which have been implicated in intercellular adhesion phenomena. This observation suggests that FHA repeats may be involved in the adhesion of B. pertussis cells to the respiratory tract.