New Worlds: Artificial viral shells could be useful nano-containers

The viral capsid combines protein units into a tiny sphere with a relatively roomy interior.

By JUDY SIEGEL-ITZKOVICH
nanotech 88 (photo credit: )
nanotech 88
(photo credit: )
Inspired by the shell that encloses the genetic material in viruses, researchers at Haifa's Technion Institute and The Scripps Research Institute in California are designing an artificial viral shell as a "nano-container" for pinpoint drug delivery, molecular computing components and a variety of other applications. Technion chemist Prof. Ehud Keinan and colleagues were inspired by the construction of natural viral capsids, which enclose a virus's genetic material within a sphere "knitted" together from identical protein building blocks. Like a soccer ball - or its nano-equivalent, the carbon buckyball (named for architect Buckminster Fuller, who designed buildings with such structures) - the viral capsid combines these protein units into a sphere with a large surface-to-volume ratio, that is, a tiny sphere with a relatively roomy interior. These design features, combined with the fact that viral capsids assemble themselves with little prompting, make the capsid an excellent model for artificial nano-capsules, the researchers report in the Proceedings of [US] National Academy of Sciences. Artificial capsids could act as "cargo containers" that deliver drugs to targeted areas, vessels that shuttle replacement genes to their new homes in the genome as part of gene therapy, or tiny enclosed labs for doing chemical reactions or building molecular computer parts. Keinan said the size of artificial capsids"is very important. "It will determine which molecules we'll be able to pack inside the container. Small containers will allow for drug delivery, big ones for delivering proteins and very big ones for the delivery of genes." The researchers decided to analyze the structure of viral capsids to learn exactly how their parts come together. They built a handful of pentagonal tiles with magnetic edges that mimic the chemically-bonding edges of natural capsid proteins. In some of their first experiments, they simply shook the magnetic tiles together in a plastic jar and watched the pieces snap together to form a sphere. "Although intellectually, we knew that this type of self organization occurs spontaneously, watching it happen from random shaking on the macroscopic scale was inspirational," Keinan and colleagues write in their paper. The researchers then turned to computer simulations of capsid construction, working with the dish-shaped chemical compound called corannulene. Also called the buckybowl, corannulene has a five-sided symmetry and rigid curve that makes it a potentially good building block for an artificial capsid. In the simulations, Keinan and colleagues experimented with different chemical "sticky edges" to the corannulene building blocks to determine the conditions under which the corannulene units would self-assemble into a ball. They created a half-sphere in the simulation, and expect to have a full sphere soon. By applying different kinds of chemical bonds at the sticky edges - from weak hydrogen bonds to metal bonds to strong disulfide bonds - the researchers believe they can alter the strength of the capsid and affect the conditions under which it assembles or disassembles. Although the researchers have yet to build an artificial capsid in the lab, "the present study gives us confidence that we can design molecules based on these principles that can assemble into chemical capsids," they write. MODEL SALESPEOPLE If you've ever noticed that a store has only good-looking employees, it may be because the owners are on to something. Shoppers - at least Canadians - buy more from attractive salespeople, according to a new study by a University of Alberta researcher. Chief investigator Prof. Jennifer Argo found clothing was rated more desirable if it had been touched or worn by an attractive member of the opposite sex, and some people said they would pay more for the item, even if it hadn't been washed. "We found that if a shirt had been touched by someone who is highly attractive and of the opposite gender, shoppers evaluated the products higher, and were willing to drop more money on it," said Argo, who studied responses from 300 people. The study has been published in the Journal of Consumer Research. In a previous study, she found people were less likely to purchase an item if they knew it had been sullied by someone else, and often a discounted price was necessary. "That research showed that products are seen to be contaminated if they've been touched by others, that they carry cooties, germs or some sort of negative essence, even if they're not visibly dirty." But she and colleagues wanted to see if there were ever instances where contact, also called contagion, could have a positive effect. The first part of the study involved sending men and women to a store to try on a specific unisex shirt. The experimenter called a colleague (acting as a salesperson at the store) ahead of time to notify them when a participant was to arrive. When the participant showed a picture of the shirt to the salesperson, they were told the last one was currently being tried on by another shopper in the change room - half the time someone with average looks and half the time a very attractive model. When the change room was vacated, the participant - who had seen the person exit the change room - could then try on the shirt and return to complete an evaluation. "When the shopper was of average attractiveness, the participant evaluated the shirt negatively. But if it was the opposite gender and they were highly attractive, the participants were willing to pay more." She concluded that if your sales staff are not very attractive, "at least have the staff dress well and be well-groomed."