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Science 8 October 1999:
Vol. 286. no. 5438, p. 197
DOI: 10.1126/science.286.5438.197g
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This Week in Science
Pathogenic bacteria and viruses must evade host defenses to survive; two reports show how mimicry of host protein function can aid in cell entry and interrupt immune system responses. Entry of the bacterial pathogen Yersinia pseudotuberculosis into eukaryotic cells is mediated by the bacterial outer-membrane protein invasin, which binds to host cell integrins with a higher affinity than natural substrates such as fibronectin. Hamburger et al. (p. 291) present the atomic-resolution structure of the invasin extracellular region. Comparison of this structure to fibronectin provides an example of convergent evolution. Although the proteins have different folding topologies, both form elongated structures comprised of tandem domains and have residues critical for integrin binding at similar locations. The structural comparison also reveals differences between invasin and fibronectin that might explain how the bacterial pathogen can compete with host proteins to exploit host cell receptors. Epstein-Barr virus infects epithelial and B cells and is associated with various cancers and B lymphomas. This DNA virus has a latent phase and expresses latent membrane proteins, such as LMP1, that are essential for transformation. LMP1 can interact with many of the signaling molecules that normally bind to CD40, a crucial activation signal for B cells. Uchida et al. (p. 300) report that LMP1 can mimic a constitutively active CD40 molecule and thus needs no ligation to aid in proliferation and antibody secretion of B cells. However, LMP1 blocks B cells from forming the germinal center, the site for affinity maturation and generation of memory B cells, and may increase the likelihood of viral survival.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)
