Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 194

The envelopes of some viruses, including orthomyxoviruses, herpesviruses, and poxviruses, contain integral membrane proteins that lack large external domains or possess multiple membrane-spanning segments. Among the best characterized is the influenza A virus M2 protein. This small (97-amino-acid) protein is a minor component of virus particles. In the viral membrane, two disulfide-linked M2 dimers associate to form a noncovalent tetramer that functions as an ion channel. This viral ion channel is the target of the influenza virus inhibitor drug amantadine (Volume II, Fig. 9.13). The effects of this drug, as well as of mutations in the M2 coding sequence, indicate that M2 plays important roles during both entry, by controlling the pH of the virus particle interior (Chapter 5), and release of newly assembled virus particles (Chapter 13). M2 belongs to a class of channel-creating viral proteins called viroporins, which are present in a number of other enveloped viruses, such as hepatitis C virus and Sindbis virus, but also in nonenveloped viruses like simian virus 40 and papillomaviruses.

Figure 4.22 Structural and chemical features of a typical viral envelope glycoprotein shown schematically. The protein is inserted into the lipid bilayer via a single membrane-spanning domain. This segment separates a larger external domain, which is decorated with N-linked oligosaccharides (purple) and contains disulfide bonds (green), from a smaller internal domain.