CHEMICAL & ENGINEERING
NEWS OF THE WEEK JANUARY 6, 2003 - EDITED BY JANICE LONG & STEPHEN TRZASKA
S C I E N C E
DNA DETECTION MADE SIMPLE Self-amplifying signal enables sensitive DNA detection without PCR T h e system consists of a single-strand D N A that covalently tethers an enzyme t o its inh i b i t o r . A s long as t h e D N A strand remains unpaired, t h e inh i b i t o r lies docked in t h e enzyme's active site. Pairing of the D N A strand w i t h its complem e n t releases t h e inhibitor, freeing t h e active site t o act on the enzyme's substrate a n d p r o d u c e an optical signal. Inactive Active enzyme enzyme Ghadiri and coworkers have proven Complementary the concept with a DNA Substrate system consisting of Inhibitor a single D N A strand Substrate bound at one end to the Bacillus cereus enSingle-strand zyme called cereus DNA neutral protease and at the other end to its small-molecule inRESPONSIVE Pairing of complementary DNA strands hibitor. F o r signal removes inhibitor from enzyme's active site, turning on an p r o d u c t i o n , t h e reoptical signal. searchers incorporated a fluorophore into t h e enzyme's substrate. W h e n e v e r a substrate over many substrate molecules, molecule is converted t o proda single molecular-recognition ucts, a fluorescence signal is proevent is automatically amplified. duced, amplifying as the enzyme This approach t o highly senturns over multiple copies of the sitive D N A detection was conceived and executed by chemsubstrate. In this way, Ghadiri istry professor M . RezaGhadiri and coworkers have detected a and coworkers Alan Saghatelian, D N A sequence of about 10 femKevin M . Guckian, and Desiree tomoles in less than three minA. Thayer at Scripps Research utes under physiological condiInstitute and Skaggs Institute tions \J.Am. Chem. Soc, 125,344 for Chemical Biology, with sup(2003)}. p o r t from t h e Office of Naval " T h e work opens t h e way t o Research. D N A detection without prior"
A
N E W S E M I S Y N T H E T I C SYS-
tem detects very low concentrations of D N A without much ado. W h e n a D N A strand encounters its sequence-specific c o m p l e m e n t , t h e i r pairing activates an e n zyme t h a t t h e n acts o n a substrate, generating an optical signal. Because t h e enzyme turns
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amplification by polymerase chain reaction (PCR), according t o Eric V. Anslyn, a chemistry professor at t h e University of Texas, Austin. W i t h most techniques for detecting very low concentrations of D N A , P C R is required to amplify the amount of D N A . However, P C R — w h i c h r e q u i r e s reagent manipulation and thermal cycling—is n o t only technically d e m a n d i n g b u t also vul-
nerable to contamination. T h e system designed by Ghadiri and colleagues, on t h e o t h e r hand, requires minimal technical k n o w - h o w and will p r o d u c e a signal only in the presence of the D N A s e q u e n c e t h a t it is d e signed to detect. "Rationally designed intrasterically regulated enzymes may constitute a promising new class of reagents for highly sensitive, rapid, and PCR-independent onestep detection of label-free D N A sequences," the researchers note. Ghadiri believes t h e system has potential for point-of-care diagnosis of diseases due t o D N A defects or infectious agents. "It was meant to detect D N A in situations where you urgently need t o k n o w t h e answer," h e tells C & E N . —MAUREEN ROUHI HTTP://WWW.CEN-ONLINE.ORG
