Interactions of Viruses with Functionalized Polystyrene Beads

Adsorption experiments of viruses Babanki and Kedougou on polystyrene derivatives were performed by incubating purified radiolabeled viruses (various concentrations) with polymers, for 10 min at room temperature, under gentle stirring. Indeed, kinetic studies have shown that the adsorption rate of viruses onto polymers reached a plateau value within 10 min of incubation time and stayed constant until 60 min where a little decrease was observed. After several washings with culture medium, polymer suspension was P counted. The bound radioactivity was then directly related to the infectious titer. Bound virus particles onto PS-SO2D vs. free virus are shown in Fig. 7. Results showed that it was

TABLE 2 Chemical Composition of Modified Polystyrene Beads Obtained from Elementary Analysis and Surface Area Calculated from Bovine Serum Albumin Adsorption

PS

PS-SO3Na

PS-SO2AA

Molar ratio

Surface

Polymer

(%)

(%)

(%)

R = COO-/(COO- + SO3-)

Sa (cm2/mg)

PS-SO2R

PS-SO2R4

33

63

4

0.06

0.44

PS-SO2R13

32

55

13

0.19

0.17

PS-SO2R20

28

52

20

0.29

0.10

PS-SO2R38

26

36

38

0.52

0.18

PS-SO2D

PS-SO2D8

16

76

8

0.18

3

PS-SO2D15

21

64

15

0.32

2.4

PS-SO2D29

24

47

29

0.55

1.1

PS-SO2D42

30

28

42

0.75

0.4

PS-SO2D48

32

20

48

0.83

1.8

PS-SO2D50

19

31

50

0.76

1.3

PS-SO2D55

23

22

55

0.84

0.6

PS-SO2F

PS-SO2F10

27

63

10

0.14

0.8

PS-SO2F21

34

45

21

0.32

4.1

PS-SO2F30

30

40

30

0.43

3.4

PS-SO2F46

24

31

46

0.60

4.2

PS-SO2F63

24

13

63

0.83

3.6

PS-SO2S

PS-SO2S7

21

72

7

0.09

2.6

PS-SO2S16

20

64

16

0.2

0.9

PS-SO2S24

28

48

24

0.33

1

PS-SO2S44

18

38

44

0.54

0.6

PS-SO2S53

19

28

53

0.65

0.6

PS-SO2S62

14

24

62

0.72

1.1

PS-SO2S72

3

25

72

0.74

0.9

PS-SO2N

PS-SO2N15

25

60

15

0.2

2.8

PS-SO2N27

24

49

27

0.36

3

PS-SO2N35

17

48

35

0.42

1.4

PS-SO2N36

23

41

36

0.47

1.7

PS-SO2N40

25

35

40

0.54

1.6

PS-SO2N42

19

39

42

0.52

1.7

PS, styrene unit; PS-SO3NA, sodium sulfonate styrene unit; PS-SO2AA, styrene unit substituted with sulfamide amino acid—R (arginine), D (aspartic acid), F, (phenylalanine), S (serine), N (asparagine).

PS, styrene unit; PS-SO3NA, sodium sulfonate styrene unit; PS-SO2AA, styrene unit substituted with sulfamide amino acid—R (arginine), D (aspartic acid), F, (phenylalanine), S (serine), N (asparagine).

FIG. 7 Adsorption of Babanki virus onto polystyrene beads substituted with aspartic acid. Each point is the mean value of triplicate data.

impossible to reach and determine polymer's maximal adsorption capacities (Bmax) for viruses as well as affinity constant. Indeed, the observed straight line (Fig. 7) corresponded to the tangent to origin of isotherm and did not present any further plateau value corresponding to the saturation of the surface. The equation of the straight line can be derived from the isotherm equation:

where B represents the concentration of bound viruses onto polymer surface and F the concentration of free viruses in solution; assuming that B << Bmax; therefore B = (K* Bmax) * F.

In order to compare the virus adsorption level of the different functionalized polymers, we defined the polymer adsorption rate of virus (expressed as % per cm2) "equaling (K*Bmax) * 100". Results presented in Fig. 8a and b indicated that the adsorption curves was similar for both viruses and that the adsorption rate was dependent on the chemical composition of the polymer. Indeed, two different behaviors of polystyrene derivatives were observed:

1. The adsorption rate of viruses varies with the chemical composition of the polymer. This is the case for arginine- and aspartic acid-substituted poly-

FIG. 8 Adsorption rate in percent per square centimeter of viral particles vs. the chemical composition of the functionalized polystyrene beads. (a) Adsorption rate of Babanki virus; (b) adsorption rate of Kedougou virus.

styrene derivatives, PS-SO2R and PS-SO2D. Moreover, these two polymers presented a maximal adsorption rate for a given composition of the polymer. The maximal rates were obtained for PS-SO2R20 which correspond to 20% of arginine substitution and R value = 0.29, and for PS-SO2D42 which correspond to 42% of aspartic acid subtitution with R value = 0.75. These results suggest that for these precise chemical compositions of the polymer, specific interactions are developed between viral particles and bioactive sites present on the surface of the modified polystyrene beads. 2. The adsorption rate of viruses is almost constant whatever the chemical composition of the polymer suggesting no specificity toward viral particles. It is the case for phenylalanine-, asparagine-, and serine-substituted polystyrene derivatives PS-SO2F, PS-SO2N, and PS-SO2S, respectively.

Furthermore, it is worth noting that whatever the chemical composition of polystyrene derivatives, the adsorption level of Kedougou virus (Fig. 8b) is systematically higher than that for Babanki virus (Fig. 8a). For example, the maximal adsorption rate onto PS-SO2R20 (R = 0.29) equaled 5.4%/cm2 for Ba-banki virus and 16.3%/cm2 for Kedougou virus. These results suggested that the affinity of viral particles for functionalized polystyrene beads is higher for Kedougou than for Babanki virus. Both viruses are enveloped viruses and adsorb onto polymer surfaces via their envelopee glycoproteins. Even if belonging to two different families of the arbovirus group—Togaviridae and Flaviviridae—it is likely that their envelopee glycoproteins contain similar domains and should recognize the same chemical sites on polymer surface. However, the envelopee glycoprotein of Kedougou virus seems to develop a better complementarity to the bioactive sites present on the functionalized polystyrene beads than Babanki virus.

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