vide the means to break through the target cell's membrane. John E. Johnson, a professor of molecular biology at Scripps Research Institute, La Jolla, To be infectious, any virus must break Calif., suggested the idea after his group through the membrane of the target cell solved the crystal structure of FHV. and unload its genetic material. How the The high-resolution X-ray structure membrane is breached is well under- of FHV shows that the cleaved peptides stood for viruses with envelopes, such are sitting just inside the surface of the as those that cause flu or AIDS. But how virus particles, Johnson says. Coupled viruses that have only a protein coat with the earlier finding that cleavage (capsid) surrounding their nucleic ac- of capsid proteins is required for FHV id—including nodaviruses and the vi- to be infectious, it suggests that the ruses that cause polio and the common cleaved peptides have to be released for cold—permeate membranes to deliver infection to occur. "We put forward the their genetic material has been unclear. idea that these peptides would be the Now, experimental support has been way to get the RNA across the memobtained for a proposed mechanism of brane," Johnson says. "But we didn't infection of nodaviruses, which are have any idea what the details were." among the simplest animal viruses. The Experiments in the lab of Scripps mechanism, based on studies of the chemistry professor M. Reza Ghadiri Flock House nodavirus (FHV), sug- now establish that the cleaved peptides gests that small peptides cleaved from have potent membrane activity: They bind the capsid proteins after the virus has strongly to membranes, forming pores assembled and packaged its RNA pro- that allow material to pass through [Chem. Biol, 6,473 (1999) ]. The findings support a mechanism of transfection that involves expulsion of a small peptide into the target cell's membrane to make it permeable for the passage of virus RNA These results are "just a small part of a big puzzle," Ghadiri says. 'The next step is to show that the reason the virus ejects these small peptides and that they alter the membrane is to allow RNA to get across," Johnson says. L. Andrew Ball, a virologist and professor of microbiology at the University of Alabama, Birmingham, notes that the Scripps work is the first to establish that these cleaved peptides have the properties they would need to perform their putative function. And Mark J. Young, a virologist and professor of plant sciences and microbiology at Montana State University, Bozeman, says the study provides convincing evidence of a dynamic structural transition to create a pore through which viral nucleic acid can move from the virus into the cell. Young also suggests that the work may have implications beyond delivery of genetic materials Scripps researchers propose that the Rock House from nonenveloped viruses to nodavirus, which packages RNA in an icosahedral cells. 'This process will undoubtcapsid structure (top, only half is shown), cleaves the surface proteins to release helical cleavage edly become a target for developpeptides (center) that subsequently insert into the ing new antiviral therapies," he membrane of the host cell (bottom). says. "And it brings forth the excit-
Breaking into c e l l s how some viruses do it
ing possibility of developing a new mechanism for gene delivery in general, by taking advantage of these pores and engineering them so that you don't just deliver a viral nucleic acid, but a nucleic acid of your choice to a target cell of your choice." To establish the properties of the cleaved peptides, Ghadiri's team—graduate student Dennis T Bong and postdoctoral researchers Claudia Steinem and Andreas Janshoff—synthesized and studied the part that they believed would be membrane active. This subunit, which they call the y1 peptide, is helical. In binding to the membrane, it creeps sideways, rather than inserting vertically. The Scripps researchers believe that several such insertions create an umbrella that pokes a hole in the membrane. Maureen Rouhi
Congestion follows Northeast rail breakup Rail woes for chemical producers have shifted to the Northeast, following the integration of Conrail rail lines into Norfolk Southern (NS) and CSX railroads on June 1 (C&EN, June 7, page 11). The service problems are not as severe as those that occurred after the railroad merger on the Gulf Coast, but many chemical firms are complaining about congestion delays, particularly in Pennsylvania, Ohio, New York, and Indiana—where many of their customers are located. "A lot of chemical companies are having problems with delayed shipments, lost railcars, and empty cars not coming back," says Michael Heimowitz, a distribution team member at the Chemical Manufacturers Association. "There have even been some chemical plant and customer shutdowns," he notes. CSX and NS admit that integration of the Conrail lines did not go as smoothly as they had hoped. Both had computer problems in early June and are adding resources to recover from that period. Chemical shippers place unique logistics demands on railroads and their computer systems that route and track railcars. Most chemical companies own or lease railcars and require that they be returned empty. In addition, plastics producers use their railcars for storage, often parking them on railroad property for later shipment. These practices make chemical companies particularly vulnerable to service disruptions. Of particular concern are railcars JULY 5,1999 C&EN
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