Scientists often discover disease-fighting compounds in all sorts of weird and wonderful places. Anti-cancer molecules have been found in corals and wasp venom of all places, and antibacterial agents have been sourced from the bright blue blood of horseshoe crabs. Now, to add to this bizarre list, it turns out that bananas might soon be added to our antiviral armamentarium.
Sounds odd, but bananas produce a particular carbohydrate binding protein – lectin – called BanLec that sticks to cell structures, or glycans, containing the simple sugar mannose. Like other lectins that target the same thing, BanLec functions as a so-called “T cell mitogen,” meaning it stimulates cell division in this type of immune cell upon binding.
Conveniently for scientists, certain viruses, like HIV, also contain similar sugar molecules on their surface, and when BanLec grasps onto them it effectively acts as a barrier to cell entry, meaning the virus can’t get inside and steal the host’s machinery to replicate. But there is a catch (of course): prompting immune cells to divide in the presence of infection can lead to systemic inflammation and actually worsen the infection as it provides the virus with a greater pool of susceptible cells to infect and thus transmit to others.
So what scientists from the University of Michigan decided to do was tinker with BanLec to see if they could separate the antiviral and mitogenic effects of this lectin without compromising its beneficial activities. Combining molecular and sophisticated imaging techniques, the team discovered that just one simple substitution in the protein’s building block, or amino acid, sequence significantly reduced BanLec’s mitogenicity yet preserved its broad-spectrum antiviral activities.
BanLec actually needs to simultaneously stick to two receptors on T cells to exert its mitogenic effects, and what this amino acid trade did was prevent this so-called “cross-linking” of receptors while still allowing binding to the cell. And when the team tested it out in vitro, they found that the modified protein was able to prevent not only HIV from getting inside cells, but also hepatitis C and influenza viruses.
“One major advantage of designer lectins lies in the fact that the risk of resistance is lower, because glycans cannot be altered as easily as protein structures,” study author Hans-Joachim Gabius from Ludwig-Maximilians-University said in a statement.
And that is a particularly desirable feature for viruses that have a tendency to rapidly mutate and evade drug treatments. But whether or not the molecule is safe or effective in humans remains to be seen, so hopefully they can push forward with further studies to find out.
The work has been published in the journal Cell.