02-principle病毒学virus巴斯德研究所.ppt

Icosahedral Symmetry Flu C HEF Flu A HA The core fusion modules Figure 3-5 Organization of the protein shell of picornaviruses. A: Subunit packing. Upper left: The order of domains in the precursor polypeptide chain. The cleavages between VP0 and VP3 and between VPP3 and VP1 are performed by a viral protease; the cleavage of VP0 to VP2 and VP4 is autolytic. Each subunit contains a jelly-roll b-barrel (trapezoidal solid), with highly variable loops and long N- and C-terminal extensions (curved lines). Two protomers (VP1, VP2, VP3, and V4) are shown in more detail in the center of the diagram. Distinct line qualities are used for each type of subunit. The diagram on the right is an “exploded view” of the right-hand protomer in the packing diagram. B: Schematic diagram of the folding of a polypeptide chain into a jelly-roll b-barrel. The strands are lettered in the order of their sequence in the chain. Strands B, I, D, and G form one sheet; C, H, E, and F, the other. The interstrand loops are designated BC, CD, etc. In picornaviruses and T=3 plant viruses, there are usually a-helices in the positions, shown as a cylinders. C to E: Ribbon diagrams of the jelly-roll cores of VP1 to VP3 of poliovirus. The numerals show residue numbers in each chain. Note how the loops give each subunit distinct characteristics. There is no evident sequence similarity, despite the similarity of fold. The small, curved arrow in C points to the entrance of a hydrophobic channel in the b-barrel, where various antipicornaviral drugs bind, blocking one or more steps in viral entry. Figure 3-4 Left: Diagram of the packing of 60 protein subunits in the shell of a parvovirus. The trapezoids represent a jelly-roll b-barrel domain (see Fig. 5) that forms the core of each subunit, and the ovals represent loops, emanating from the jelly-roll domain, which form contacts about the threefold axes. Right: Ribbon diagram of the folded subunit of canine parvovirus, viewed perpendicular to the fivefold and