New clues to protein structure/function Studies of the interactions involved in protein folding are shedding light on fundamental aspects of protein structure and activity relationships and providing clues about how to engineer proteins with new prop erties, according to speakers at a symposium sponsored by the Divi sion of Biochemical Technology (for merly the Division of Microbial & Biochemical Technology) at the Mi ami Beach meeting of the American Chemical Society. One speaker at the symposium, David E. Wemmer, an assistant chemistry professor at the Univer sity of California, Berkeley, and fac ulty associate at Lawrence Berkeley Laboratory, described research in which apamin, a small, neurotoxic peptide component of honeybee venom, provides a framework to sta bilize the α-helical structure of an other peptide. The research demonstrates that when the amino acids that make up what is known as the S-peptide, a well-characterized segment of the enzyme ribonuclease-A (RNase-A), are incorporated into apamin they take on a structure very similar to their structure in native RNase-A. The S-peptide /apamin hybrid binds to S-protein (the large fragment of RNase-A from which S-peptide was cleaved) and restores the enzyme's activity, Wemmer says. The hybrid also elicits antibodies that recognize both the hybrid and native RNase-A. Apamin is a small, highly stable protein. It contains 18 amino acids. Its stability derives from two disul fide bonds and significant secon dary structure, including an α-helix at the C-terminal end of the protein. In work supported by the Na tional Science Foundation, Wemmer and graduate students Joseph H. B. Pease and Richard W. Storrs creat ed hybrid proteins that consist of the eight N-terminal amino acids of apamin (which include two cyste ine residues) and 12 or 19 residues of S-peptide. The chemists replace two S-peptide amino acid residues with cysteine residues to retain the two disulfide bonds found in apamin. Despite the changes, the first 12
residues of the S-peptide fragment adopt a stable α-helical conforma tion in the hybrid, Wemmer says. Both S - p e p t i d e / a p a m i n h y b r i d s complement S-protein, strongly suggesting that the S-peptide adopts a conformation very similar to its conformation in native RNase-A. Preliminary results with two other peptide/apamin hybrids suggest that these peptide fragments also adopt α-helical structures similar to their native conformations. Such hybrids may prove useful in examining structure-function re lationships for many biologically ac tive sequences, Wemmer says. There is also the possibility that such con structs might provide a route to new vaccines. S-peptide alone, for ex ample, would be degraded in vivo before it could stimulate an immune response. The S-peptide/apamin hy brid possesses sufficient stability to elicit such a response. In the anti body research, Wemmer collaborated with Peter S. Kim of Whitehead In stitute for Biomedical Research. Rudy Baum
Use of environmental expert systems growing Environmental expert systems are increasing rapidly in number, ap plications areas are expanding, and the systems have begun to attain greater acceptability in the environ mental community as decision making tools, says Judith M. Hushon, head of artificial intelligence and information systems at Roy F. Weston Inc., Washington, D.C. Hushon pre sented her assessment at a Division of Chemical Information symposium on environmental expert systems that she organized at the recent American Chemical Society nation al meeting in Miami Beach, Fla. Hushon points out that although the first such systems came out only about five years ago, almost 70 are being used today or are in various stages of development. In addition, she says, "Whereas a number of the early systems took on very limited areas of expertise, such as the oper ation of a sewage treatment plant, the systems are now moving out to tackle siting problems and recom
mendations of complex remedial technology combinations/' She adds, "What is even more important is that expert systems are becoming an accepted vehicle for offering advice for solving environ mental problems. Over the next few years, more complex systems will be developed that share databases and tackle multiple related environ mental problems." Expert systems help solve prob lems in well-defined subject areas based on information provided by experts. To develop a system, a "knowledge engineer" questions ex perts in the field in an effort to identify the kinds of information needed to solve the problems being modeled and how this information is used to derive conclusions. This information is then programed into the system's "knowledge base." A separate "inference engine" pro vides mechanisms for interpreting commands and accessing the knowl edge base to solve problems. Initially, most expert systems were developed on microcomputers, but there has been a steady growth in the number of workstation- and minicomputer-based systems as ex pert systems have grown more so phisticated. IBM PC-ATs and com patibles are still the most common development base. "However," says Hushon, "the limit of 640K of ran dom access memory [on AT-class computers] is causing programers
Hushon: greater acceptability October 9, 1989 C&EN
25
