Researchers have found that a protein found in tamarind seeds reduces the infectivity of chikungunya virus by 64% and the virus RNA levels inside infected cells by nearly 45%. Based on the promising results obtained through in vitro studies, the researchers are planning to test the protein on animals to prevent and/or treat chikungunya infection. Currently, there are no drugs to treat chikungunya or any vaccine to prevent it.
The study published in the journal Virology has for the first time confirmed that the sugar moiety on the surface of alphaviruses has a role in infectivity; this is known for other viruses such as HIV and influenza.
The team led by Shailly Tomar from the Department of Biotechnology at the Indian Institute of Technology (IIT) Roorkee found the tamarind protein (tamarind chitinase-like lectin or TCLL) binds to the sugar moiety (N-acetylglucosamine or NAG) present on the surface of chikungunya virus. When TCLL protein binds to the NAG sugar moiety it nearly coats the virus particles thus preventing the virus from binding with the receptors on the host cells. Since binding to the host cell receptors, which is the first step in the infection process, is nearly prevented, the ability of the virus to infect the host cells is compromised.
Based on structural studies carried out by Pravindra Kumar’s team at IIT Roorkee it became clear that the TCLL protein specifically binds to NAG sugar molecules. “Since tamarind seeds are traditionally used in Ayurveda to treat many ailments and conditions, we wanted to know the molecules in the seed. Two proteins were found in abundance. Based on amino acid sequence, we found one protein has both anticoagulant and blood thinning properties while TCLL, which is a lectin protein, binds specifically to NAG sugar molecules,” says Prof. Kumar, who is a coauthor of the paper.
“We wanted to study if TCLL binds to chikungunya virus through the NAG moiety. Our hypothesis was that if the TCLL protein binds to NAG, the virus will not be able to attach and interact with host cell receptors leading to less infection,” Prof. Tomar says.
The team first demonstrated the ability of the TCLL protein to bind to the NAG sugar moiety found on chikungunya and Sindbis virus, which too belongs to the alphavirus genus.
Binding of TCLL to chikungunya virus through the NAG sugar moiety was then confirmed by first treating the protein with the NAG molecule and then incubating the NAG-treated protein with the virus. “We found that the NAG molecule binds to the TCLL protein and prevents the protein from binding to the virus,” Prof. Tomar says. “This helped confirm that TCLL binds to chikungunya virus through NAG.”
They found that chikungunya virus treated with the TCLL protein showed nearly 64% reduction in the ability to infect host cells. But in the case of NAG-treated TCLL, the reduction in chikungunya virus infectivity was just 14%. “Like antibodies that bind to the virus surface and neutralises or prevents the virus from binding to the host cells, the TCLL protein binds to NAG and prevents the virus from interacting and infecting the host cells,” she says.
TCLL protein of different doses was incubated with the virus for different time periods. They found that 100 micromolar of the protein incubated with the virus for just 30 minutes was sufficient to cause 64% drop in infectivity.
Explaining why only 64% reduction in infectivity was seen when the virus was treated with the protein, Ramanjit Kaur from IIT Roorkee and first author of the paper explains: “Besides NAG, there could be other sugar molecules through which the virus interacts with the host cells. Also, there may be other receptors on the host cells which allow the virus to get into the cells.”
The antiviral effect of the protein was also assessed by measuring the RNA levels inside the infected cells. Treatment of the virus with TCLL led to a reduction of 45% chikungunya RNA levels inside the host cells.
“The TCLL protein can bind to glycan found on nearly 30 members of the alphavirus genus. So the finding of this study has huge implications,” Prof. Tomar says. Based on the findings of this work, Prof. Tomar and Prof. Kumar have filed a patent for chikungunya antiviral composition consisting of TCLL protein.