Scientists from Corning’s biochemical technologies unit have developed a new approach for displaying functional membrane proteins on surfaces that may allow for the rapid screening of drug targets against this important class of “druggable” proteins. Their paper, published in the March 20 issue of Journal of the American Chemical Society, is the first demonstration of a protein membrane array and how it might be used in ligand screening, the researchers said.
To generate their protein arrays, the scientists spotted membrane preparations derived from cell lines that each overexpress a specific G protein-coupled receptor (GPCR) onto glass or gold substrates coated with gamma-aminopropylsilane (GAPS). This surface differs from the GAPS-coated slides Corning currently markets to DNA microarray researchers.
“The trick of the trade is in the types of GAPS that we have,” said Joydeep Lahiri, the paper’s corresponding author and leader of the company’s high sensitivity assays group. Corning has applied for a patent on the technology, he added.
Not only were these arrays remarkably stable — at least for two months — but more importantly, the GPCRs were functional in binding assays with ligands and inhibitors, the paper shows. Moreover, the assays were able to distinguish between three types of adrenergic receptors, based on their affinities. In theory, any membrane protein could be deposited and assayed in this way.
“On the one hand, it’s deceptively simple, and on the other hand, it clearly works very well,” said Jonathan Blackburn, chief scientific officer of Sense Proteomic, a microarray company based in Cambridge, UK, which also works on functional membrane proteins. But the article is mostly a proof of concept, he believes. “It demonstrates what’s possible, but there is a lot of work to be done to take this forward,” Blackburn said.
Membrane Proteins Hard To Get, But Key in Screening
Because membrane proteins, and GPCRs in particular, are some of the most important drug targets to date, the obvious application for the arrays would be in drug screening, especially against receptor subclasses and orphan receptors. Other potential uses, according to Lahiri, are studies of protein-protein interactions and assays that “go beyond just binding of ligands,” by which he most likely meant signal transduction events.
However, one of the major limitations to developing the membrane protein arrays further is the lack of protein content. In its publication, Corning used only commercially available membrane preparations, and isolating membrane proteins is still considered a significant problem. “There are whole consortia out there trying to express as many GPCRs as possible and finding it very difficult,” said Blackburn.
Nevertheless, Corning said it has already been approached by several content providers, and is hoping to collaborate with a small number of them in the future. “We would like to identify potential partners, probably over the next few months,” said Donald Munroe, business development manager at Corning Life Sciences. But he added that Corning is not in any hurry to mass market GPCR chips. The company’s caution follows an aborted attempt to bring to market a high-density cDNA chip last year.
In order to commercialize the technology, Lahiri and his team are currently validating the published data and expanding the scope of the method. “It certainly works for different kinds of membrane proteins, and it also works for different kinds of lipids,” Lahiri said, adding that since submitting the paper his group has constructed arrays containing the EGF receptor.
Early-access partnerships with pharmaceutical companies, which would double as content providers, are likely to follow. “At this point we are far more interested in learning and establishing key relationships than we are in selling to every lab across North America,” said Munroe, but he left open the possibility of marketing the technology more widely later on.
— JK