Teaching DNA to do chemistry
says. These compounds intercalate into double-stranded DNA a process that might be mimicked by taking advantage of the doublestranded regions of single-stranded aptamers, she explains. Bhatnagar Kotia's early work in this area has been promising. She haa sshwn that G-quartet aptamers interact with some PAHs but not with others, suggesttng that they could be used to discriminate among various compounds. McGown also sees aptamers as valuable for studying the nature of binding. 'We know that the G-quartet binds to thrombin," she says. "But we don't know whether it recognizes a three-dimensional structure or has a preference for a particular amino acid, or if a particular base in the G-quartet is responsible." The G-quartet structure of the DNA ligand Because it is so easy to make changes that binds to thrombin. to an aptamer, it is a good tool for probing these possibilities, says McGown. There's different ways or with different strengths, no need for a complicated chemical syntheallowing the separation of metals." sis each time you want to try something Clark found that the addition of lannew. And the changes can be very subtle— thanide ions reduced the melting temperature of the tb ligand, indicating the destabi- perhaps just a single base. "It's marvelous," she says, "like working with Legos." lization of the G-quartet. She also observed energy transfer from Tb3+ to the tb ligand With each change, you can find out how and to a variant she designed, which binding is affected, McGown explains. showed an even larger difference in inter"Then you can take these little clues and actions among the metal ions. build them into something bigger—perAptamers could even be used wiih polycy- haps a better understanding of how chemiclic aromatic hydrocarbons (PAHs)) McGown cal recognition works in thefirstplace."
Linda McGown is teaching DNA to do analytical chemistry. The Duke University researcher and her students are employing short oligonucleotides known as "aptamers" or "nucleic acid ligands" tofindnew solutions to old chemical problems such as chiral separation or selective binding of metals. Aptamers are single- or double-stranded pieces of DNA or RNA, usually 15-40 bases long. They work by binding target molecules, such as proteins, with high affinity and specificity. Researchers recognized the medical and pharmaceutical potential of these interactions years ago, launching large-scale screening of combinatorial libraries tofindaptamers that might be valuable for applications such as inhibiting HIV infection. McGown likens this screening process to the evolution of molecular recognition in antibodies. Both processes rely on the interaction of me host's diree-dimensional structure with the target. But aptamers are easier to work with than antibodies, she says. They can be synthesized quickly by automated processes and can be accurately reproduced. Chemical modifications, such as the addition of a dye, are simple. Attachment to glass surfaces or beads is also easy. McGown and graduate students Ruchi GOVERNMENT AND SOCIETY Bhatnagar Kotia and Elizabeth Clark are focusing their work on a single-stranded DNA aptamer structure called the G-quartet. CRMMA resurfaces house for people outside of the organizaThe structure is named for a cluster of four After sitting quietly for several years, the tion who have questions regarding chemiguanines that come together in the folded Chemical Reference Material Manufactur- cal reference materials, CRMMA is a forum structure—which looks like an arch with a for its members to discuss issues that imers Association (CRMMA) is back in the hook at each end—to form an imaginary pact the reference materials business. spotlight and ready for action. But before square. The G-quartet is the basis of the it can begin tackling larger issues, the For example, CRMMA is putting tothrombin-binding (tb) ligand that the association must address the first item on gether a position paper on the NIST/EPA group studies. its agenda—improving the image of the proficiency testing (PT) program. In the "Aptamers have a lot of analytical potenorganization. past, EPA provided drinking water- and tial," McGown says. "They are essentially CRMMA is viewed by many as having a wastewater-testing laboratories with free sensors—highly selective for a particular PT samples. Because of budget constraints, negative, defensive posture. Some compaanalyte." For example, Bhatnagar Kotia sep- nies joined CRMMA because they perceived EPA moved its water PT studies to the priarated D-Trp from D-Tyr using capillary elec- a need to protect their own interests rather vate sector (Anal. Chem. 1198, 70, 262 A). trochromatography, with a 20-base variant of than those of the industry as a whole, says Now, labs must purchase PT samples from the tb ligand attached to the fused-silica cap- CRMMA President Chuck Wibby of Envicommercial PT providers. In 1997, NIST illary column. She also achieved the more ronmental Resource Associates. The organi- was chosen to be the overseer of these PT difficult chiral separation of D-Trp from L-Trp zation is now undergoing a face-lift, hoping providers. Issues such as which analytes to with the same column. include in the PT samples, whether states to promote more of a positive image. 'We should select the provider (s) and legal Aptamers might serve other purposes. are trying to educate people that there is an liability for PT providers are considered in "I thought it would be interesting to see if organization that experts in reference matethe paper these sequences would bind to families," rials belong to, so that otiier organizations McGown says. "Why wouldn't it be possithat need help with reference materials can CRMMA is also working with the U.S. ble for some of them to bind to metals, for access our expertise," says Wibby. Department of Transportation (DOT) and example? Different ions would interact in the International Air Traffic Association In addition to serving as a clearingAnalytical Chemistry News & Features, May 1, 1999 3 1 3 A
News
(LATA) on hazardous materials shipping regulations. Reference materials manufacturers commonly run into problems shipping samples internationally because of differences in regulations overseas. CRMMA is trying to unify the regulations so that samples shipped under DOT regulations will be accepted by IATA. More information on CRMMA can be obtained at its new Web site (www.crmma.org). Britt Erickson
Unified protection The European Union (EU) has moved one step closer to unified patent protection for inventions filed in member states. The move will avoid the present costs and problems to inventors of having to file individual applications for each country. The measures were described in a policy communication adopted by the European Commission in February 1999, which aims to promote innovation by simplifying the patent process. In June 1997, the commission published its Green Paper on patents, in which an action plan for innovation in Europe and the single market was outlined. The paper asked whether the patent system in Europe should be improved and modernized. It seems obvious now that the answer would be "yes"i given that 12 member states were carrying out individual patent processing with different sets of rules and policies. To ensure full coverage, each patentee needed to file a separate application in each country. The introduction of a unitary patent valid throughout the EU has become a political priority arising from the demands of users to decrease costs and optimize legal certainty. According to Mario Monti, the single market commissioner who initiated the Green Paper, "This coherent policy framework lays the foundations for ensuring that pan-EU patent protection can be obtained more easily and more cheaply than at present. This will serve to promote investment in innovation, which is so crucial to employment, growth, and competitiveness in the EU." The communication calls for new regulations to be written in 1999 to create an "EU Patent", based on a single application. The system would run parallel to national patents issued by individual offices and the European Patent Office. This would provide businesses with a choice of protective systems and allow easier enforcement of patentee rights. 314 A
organization that has an interest in laboratory accreditation. Membership in NACLA, however, does not guarantee recognition as a NACLA accrediting body— all potential accrediting bodies will be evaluated. Although three applications have already been submitted, the procedures for recognizing competent accrediting bodies are still being finalized. The organizational structure of NACLA is also evolving and now includes a board of directors as well as an operations council. Previously, the U.S. Department of Justice ruled that federal employees can serve on the board of directors of standards organizations, such as NACLA, but only in a limited capacity. As a result, federal participants act as nonvoting liaison members. The operations council, which includes all members of the board of directors, includA proposal for harmonizing the patenting the liaison members, was added so ability of computer programs, which inthat federal government employees could cludes chemometrics, bioinformatics, and vote on issues regarding recognition laboratory information management syscedures, proficiency testing, evaluator tem software, will also be put forward betraining and technical requirements The fore summer 1999 to ensure that software operations council is charged with overcompanies can obtain effective patent proseeing applications from the accrediting tection for their inventions in all the membodies and keeping the NACLA recogniber states. At present, patent protection is tion process up to date not particularly cohesive because of the disparate approaches of each member In addition to eliminating duplicate acstate. The action will form part of the Euro- creditations, NACLA is interacting with inpean Commission's fifth framework proternational accrediting bodies, such as the gram on research and development. International Laboratory Accreditation CoDavid Bradley operation (ILAC) and the Asia Pacific Laboratory Accreditation Cooperation, to establish worldwide acceptance of credible data NACLA still seeks and agreement on common procedures. members NACLA's strengths are in evaluator training and performance monitoring. BeThe National Cooperation for Laboratory fore the general meeting, NACLA held a Accreditation (NACLA), a public-private three-day evaluator training course to partnership aimed at reducing the number bring evaluator candidates up to speed on of accreditations for U.S. testing and calibration laboratories (Anal. Chem. 1997, the NACLA evaluation process. The 69,161 A; 1998, 70, ,73 A), held its first course covered recognition procedures, annual general meeting on March 25,1999. requirements, and on-site evaluation processes. Evaluator training and perforApproval of the 1999 Board of Directors and affirmation of the NACLA bylaws high- mance monitoring are just two of the requirements for eventual ILAC recognition. lighted the agenda. Although many specifics still need to be In addition NACLA must meet several other criteria, including qualification laid out before the program is up and runregional body. Currently NACLA is not ning, NACLA's biggest concern is to build considered a regional body because it only up its membership. Currently, the number of NACLA members is disappointingly low, represents one country the United says Dave Krashes, Chair of NACLA's States In the future NACLA hopes to membership committee. Out of 5000 poten- broaden its membership to include accredtial members, only 50 were successfully itation bodies in Mexico and Canada recruited during a recent membership which will qualify it as a regional bodv drive. Efforts are under way to bring that More information on NACLA can be number up to at least 500. found at its Web site (http://ts.nist.gov/ Membership in NACLA is open to any nacla). Britt Erickson
Analytical Chemistry News & Features, May 1, 1999
