Poliovirus coat proteins

Figure 2. Tryptide analyses of poliovirus NCTPx, and a I40 kU apparent precursor to NCVPx. Bona fide poliovirus (55s) NCVPx (gel l) was isolated, and its tryptic map compared with that of the I40 kB protein isolated in zinc (0.5 mM)-treated infected cells (gel II) by two-dimensional electrophoresis (pH 2.1) and chromatography (butanol acetic acid water, 3 1 1) on cellulose thin layer plates. Other tryptic fragments in the I40 kD protein are present in poliovirus coat proteins (not shown).

HLA virus (5 [xg/ml) and their sensitivity to infection by isolated RNA was analyzed. We found (see Table 5) the cells exposed to HLA virus for one minute at 37° C prior to addition of single- or double-stranded poliovirus RNA yielded 100 times more infective centers after 15 min incubation at 37° C than untreated cells (Breindl and Koch, 1972). This result reveals that the poliovirus coat proteins are able to sensitize HeLa cells to infection by viral RNA. 

Figure 16.14 Schematic diagrams of three different viral coat proteins, viewed in approximately the same direction. Beta strands I through 8 form the common jelly roll barrel core, (a) Satellite tobacco necrosis virus coat protein, (b) Subunit VPl from poliovirus.

Many virus coats have 180 subunits or a number that is some other multiple of 60. However, in these coats the subunits cannot all be in identical environments. Two cases may be distinguished. If all of the subunits have identical amino acid sequences they probably exist in more than one distinct conformation that permit them to pack efficiently. (Next section) Alternatively, two or more subunits of differing sequence and structure may associate to form 60 larger subunits that do pack with icosahedral symmetry. For example, the polioviruses (diameter 25 nm) contain three major coat proteins (a, P, and y or VP1, VP2, and VP3). These are formed by cleavage of a large precursor protein into at least four pieces.76 77 Tire three largest pieces of 33-, 30-, and 25-kDa mass (306,272, and 238 residues, respectively) aggregate as (aPy)60. Sixty copies of a fourth subunit of 60 residues are found within the shell. 

In addition, a proteolytic activity was detected apparently synthesized in the cell-free system, which cleaved the coat precursor polypeptide of the virus into fragments matching in size the virus coat proteins produced in infected cells. In agreement with the results discussed for poliovirus, the results tend to rule out an autoproteolytic activity associated with the coat proteins. This is in conflict with an earlier study on EMC virus proteolysis (37) > in which coat polypeptide gamma, co-purified with an endo proteolytic activity. 

In summary, evidence for a poliovirus gene product participating in the proteolytic cleavage of virus coat protein includes a. kinetics of production b, characteristic pH optimum c. abolition of activity by inhibitors of virus RHA and protein synthesis d. labilization to heat inactivation by amino acid analogs after cellular protein synthesis was abolished e. in similar fashion, recovery of protease activity, after inhibition of virus proteolysis by a leucyl chloromethyl ketone, required protein synthesis f. finally, protease activity co-purified with virus non-structural polypeptide X,... 

The two known functions of the viral coat proteins, protection against RNase and specific adsorption to cells, are affected by DEP to a small (RNase resistance) or large (adsorbability) extent and in the latter case can be restored completely by addition of DEAE-dextran. But nevertheless, the infectivity of DEP-treated poliovirus is the same as that of isolated viral RNA. This shows clearly that loss of RNase resistance is not responsible for the low infectivity of the isolated viral RNA. It also appears very unlikely that the difference in adsorbability between intact virus and isolated RNA and DEP-inactivated virus is responsible for the low infectivity of the latter. However, it is possible that native virus particles enter the cell at specific membrane loci. Provided that neither loss of RNase resistance nor adsorbability are responsible for the comparatively low infectivity of naked RNA and of virus particles inactivated by heat or DEP, the viral coat proteins must have yet another function, so far unidentified. 

The tobacco mosaic virus (center right), a plant pathogen, has a structure similar to that of MB, but contains ssRNA instead of DNA. The poliovirus, which causes poliomyelitis, is also an RNA virus. In the influenza virus, the pathogen that causes viral flu, the nucleocapsid is additionally surrounded by a coat derived from the plasma membrane of the host cell (C). The coat carries viral proteins that are involved in the infection process. 

FMDY is rapidly inactivated by low concentrations ( 2 ig/nil)of proflavine in the presence of visible light. This is due to inactivation of the ENA and eventually the particles disrupt into free ENA and 12S protein subimits (4) In contrast poliovirus is relatively resistant to photodynamically active dyes and any inactivation which occurs is due to oxidation of the protein coat. This observation is yet another manifestion of the porous nature of the FMDV particles compared with those of the other genera. 

The protein coat of polioviruses consists of four different peptides with molecular weights of 32000, 30000, 28000 and 6000. They can be separated by gel electrophoresis after disruption of the virus particles by heat and SDS (Summers et al., 1965). Each virus particle possesses approximately 60 copies of every peptide. The peptides have been named "viral proteins (VP, ... 

It has been reported that hydroxylamine (HLA) inactivates the viral RNA inside the virus particle without impairing the antigenicity of the native virus (Franklin and Wecker, 1959). Exposure of poliovirus to 1 M HLA does not result in loss of viral peptides nor does it alter its sedimentation rate in sucrose or its density in CsCl. HLA-treated poliovirus adsorbs normally to HeLa cells. These results show that the HLA virus particles contain a native protein coat (Breindl and Koch, 1972). 

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