A new probe may enable researchers to identify drug resistant influenza viruses

Flu has always been a public scare issue, the latest being the “swine flu” (a.k.a H1N1 strain). One of the problems with the influenza virus is that its genome is composed of 7-8 separate pieces of RNA (an unusual case, since most viral genomes are composed of one or two pieces). These pieces can recombine among different strains creating new strains – hence the apparent low effectiveness of flu vaccines.

Other than vaccines, there is also an antiviral drug called Oseltamivir (also known as “Tamiflu”) that slows down the viral infection. It does so by inhibiting a viral enzyme called neuraminidase (NA). NA breaks down sialic acid. NA activity helps the elution and mobility of the virus particles.  However, recent years showed some flu strains that are resistant to Tamiflu.

NA belongs to a large family of sialidases that are found in many other pathogens, as well as in our own cells. Hence, understanding sialidases biology is important.

In a paper published now in PNAS, researches developed a cell permeable sialidase inhibitor. This inhibitor binds to the active site, the same site that also binds Tamiflu. The inhibitor itself is not fluorescent, so the researchers chemically conjugated it to biotin (after it bound the sialidases). They then probed the cells with fluorescently labeled streptavidin (a protein with high affinity for biotin) and could detect flu-infected cells.

Visualization of influenza-infected cells using DFSA labeling. Green: FITC-tagged streptavidin; Red (Alexa fluor 594): immuno-fluorescence with anti influenza nucleoprotein antibody; Blue: DAPI staining of nuclei. Source: Tsai C et al. PNAS 2013;110:2466-2471

Visualization of influenza-infected cells using DFSA labeling. Mock – non-infeced cells. Green: FITC-tagged streptavidin; Red (Alexa fluor 594): immuno-fluorescence with anti influenza nucleoprotein antibody; Blue: DAPI staining of nuclei. Source: Tsai C et al. PNAS 2013;110:2466-2471

They claim (but for some reason don’t show) that adding Tamiflu resulted in the absence of labeling of Tamiflu sensitive strains, but the labeling persisted for resistant strains. Hence, this method may assist in identifying resistant strains.

ResearchBlogging.orgTsai CS, Yen HY, Lin MI, Tsai TI, Wang SY, Huang WI, Hsu TL, Cheng YS, Fang JM, & Wong CH (2013). Cell-permeable probe for identification and imaging of sialidases. Proceedings of the National Academy of Sciences of the United States of America, 110 (7), 2466-2471 PMID: 23359711

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