engleski

Adenovirus type 5 with short fiber shaft domain

Adenovirus type 5 (Ad5) infects cells by attachment of the viral fiber protein to the coxackie B virus and adenovirus receptor (CAR). After attachment Ad5 is internalized through interaction of RGD motifs on the penton base with avb3, avb5 and avb1 integrins on the cell surface. The fiber protein consists of a short N-terminal tail, a shaft and a cell binding domain called knob. In human adenoviruses, the rod-like fiber shaft contains repeats of up to 14 amino acids forming b sheets, with the number of repeats ranging from 6 to 23. The goal of this study was to investigate the role of the Ad5 fiber length in CAR mediated infection. The construction of recombinant adenovirus Ad5FbD639 was performed by cloning and manipulation of the full length adenovirus genome as a stable plasmid in E. coli, using the bacterial homologous recombination machinery. This virus contains fiber of 8 b sheets, instead of the 22 b sheets in wild type Ad5. The recombinant virus Ad5FbD639 yielded plaques on 293 cells, but the spread through the monolayer was delayed compared to wild type Ad5bgal. Western blotting using polyclonal anti-fiber antibodies revealed the presence of shortened fiber. The fiber protein from Ad5FbD639 was capable of forming trimers, which was tested by nondenatured SDS-electrophoresis and Western blotting of CsCl purified viruses. Comparison of the infectivity index (the ratio of physical particles to infectious particles) of Ad5FbD639 and wild type Ad5bgal virus showed that Ad5FbD639 was 25 to 48 times less infectious than Ad5bgal. This difference in infectivity is not a consequence of amount of shortened fiber because Western blot analysis showed similar amounts of wild type and shortened fiber in virus samples normalized for physical particle number. Preliminary results obtained by flow cytometry demonstrated that Ad5FbD639 binding to CAR is not (or is slightly) reduced compared to wild type Ad5bgal, thus the difference in infectivity seems to be consequence of disturbed internalization. Several hypotheses could be proposed to explain Ad5FbD639 difference in infectivity. Deleted part of the Ad5 fiber could remove some function(s) necessary for virus maturation, or the observed weak cell infectivity of short-shafted fiber-containing Ad5 vector could be due to repulsive acidic charges carried by the capsid and present on the cell surface. It is also possible that a correct spatial arrangement of knob and penton RGD motifs is critical for efficient viral binding and entry. The RGD is positioned in the center of a protruding loop, which varies in length among serotypes. Therefore in the case of shortened Ad5 fiber the natural spatial arrangement is disturbed. These hypotheses are not mutually exlusive, and the factors described above could combine.

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