STRUCTURAL BIOLOGY OF MACROMOLECULAR STRUCTURE

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This Laboratory aims to elucidate the regulatory mechanisms that govern the folding of macromolecules and the assembly of supramolecular complexes, and underlie the synthesis of organelles, cells, and tissues. To this end, advanced methods of structural analysis based on electron microscopy and computer image processing are developed and applied. In the past year, we have applied cryoelectron microscopy and three- dimensional image reconstruction to purified capsids of herpes simplex virus, type 1, which had been biochemically depleted in vitro of certain components, reassociated with those components, or decorated with monoclonal antibodies. The results have led to a provisional localization of the four minor capsid proteins, and have implications for their likely functional roles. VP22 (40kDa) is located entirely within the shell of (precursor) B-capsids, but is eliminated when DNA is packaged: most likely, it is a scaffolding protein that is at least partly responsible for controlling the polymerization of approximately 900 copies of the major capsid protein - VP5 (148kDa) - into a large (125nm), precisely defined, icosahedral shell. VP26 (12kDa) appears to make up the pentons, with 80-100 copies of this small protein present at each of the five-fold vertices: VP26 may be involved in controlling release of the packaged DNA. VP19 (55 kDa) and VP23 (36 kDa) appear to be the triplex proteins, forming heterotrimers at the three-fold sites on the outer surface of the icosahedral surface lattice. By analogy with comparable proteins of other viruses, they probably serve to stabilize the capsid shell by reinforcing the underlying array of hexamers of VP5.