Cu-ZnO surface species are the most active form of the catalyst. They also showed that the Zn-Cu species don’t remain stable under reaction conditions. Instead, they react with oxygen and form Cu-ZnO.—MITCH
JACOBY
BIOCHEMISTRY
▸ Hepatitis B virus protein has unusual iron-sulfur cluster In a step toward understanding how the hepatitis B virus (HBV) replicates and causes infection, a research team has determined that one of the virus’s four proteins may incorporate a unique iron-sulfur cluster. Team leader Maria-Eirini Pandelia reported this discovery at the ACS meeting. The protein, known simply as X, is only 154 amino acids long and is the least understood of the HBV proteins. HBV infects the liver and can cause short-term and chronic illness. Biochemists know that X interacts with a number of proteins in host cells and that it plays a role in virus infectivity, replication, and ultimately cancer formation. However, the protein’s structure and mechanism have remained elusive. Pandelia’s team started investigating X last year, after work by another group indicated that the protein incorporates iron. Elemental and spectroscopic analysis by Pandelia and colleagues shows that the protein contains a [2Fe2S] cluster when isolated in the presence of oxygen. When reduced, the cluster converts to [4Fe4S]. Exactly how the conversion occurs is unclear. Research keeps revealing more about the diversity and importance of iron-sulfur clusters in biological chemistry, commented metalloprotein spectroscopist Joshua Telser of Roosevelt University. “It’s never-ending.”—JYLLIAN
KEMSLEY
BIOCHEMISTRY
CREDIT: ADAPTED FROM JACS
▸ Getting GPCRs into liposomes G protein-coupled receptors (GPCRs) are key drug targets and important signaling proteins embedded in cell membranes. To study the proteins’ specific signaling interactions more easily by eliminating the complexities of the cellular environment, researchers often use detergents to extract them from cell membranes and then reconstitute the receptors in synthetic
POLYMERS
New switcheroo for vitrimers
O B
O
O
B
O
Six years ago, Ludwik Leibler and colleagues developed a new type of B B plastic with some impressive propO O O O erties: It was tough like a thermoset polymer, such as Bakelite, but malleable like glass in that it could be melted and its shape reset. Leibler, of France’s National Center for Scientific Research, called the new material a vitrimer. The key to the vitrimer’s malleability was its chemistry. It consisted of ester cross-links that could break and reconnect with new partners when heated. Looking to apply this concept to polymers more commonly in use, Leibler, Renaud Nicolaÿ of the City of Paris Industrial Physics & Chemistry Higher Educational Institution, and colleagues have now switched out the ester cross-links for dioxaboralane cross-links (shown). These functional groups can be incorporated into commonly used polymers, such as poly(methyl methacrylate), polystyrene, and high-density polyethylene. When heated to 60 °C, the dioxaboralanes undergo metathesis—that is, they swap binding partners. The new vitrimers are also amenable to commercial processing methods, Leibler told attendees at the ACS meeting. The vitrimers could be processed, ground, and reprocessed several times via extrusion, compression molding, or injection molding, just like commercial thermoplastics. The research was also reported in Science (2017, DOI: 10.1126/science.aah5281).—BETHANY HALFORD
membranes. The detergents can modify ligand binding interactions and other native properties of GPCRs, so researchers must use dialysis or adsorbents to remove detergents before studying the reconstituted proteins. A team led by Neal Devaraj and Roger Sunahara of the University of California, San Diego, developed a GPCR reconstitution technique that doesn’t require detergent cleanup (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.6b12830). In the tech-
In INSYRT, GPCR-containing cells are treated with an acyl maltose thioester (step not shown), forming micelles. Native chemical ligation combines the micelles with lysolipids, forming phospholipids that assemble into GPCRcontaining proteoliposomes.
+
+ Lysolipids
Native chemical ligation
nique, called in situ lipid synthesis for protein reconstitution technology (INSYRT), the scientists use acyl maltose thioesters to extract GPCRs from cells, forming micelles containing the proteins. They then use native chemical ligation to combine acyl groups in the micelles with lysolipids, forming phospholipids that assemble spontaneously into spherical GPCR-containing proteoliposomes. The thioesters don’t survive the reaction and therefore don’t have to be removed. In a presentation at the ACS meeting, Devaraj showed that INSYRT could reconstitute the adenosine A2A receptor in proteoliposomes, where the receptor maintained its natural function.—STU
BORMAN
Phospholipids with or without GPCRs
Micelles Micelles with GPCRs GPCR-containing proteoliposomes APRIL 10, 2017 | CEN.ACS.ORG | C&EN
11
