Use of a cyanine dye as a reporter probe in reagentless maltose sensors based on E-coli maltose binding protein

Reagentless bio-sensing proteins represent a promising technology being developed for sensitive chemical detection and analysis. The majority of these sensor proteins incorporate environmentally sensitive UV-excited fluorescent dyes as reporter probes. In this report, we describe conjugation of the commercially available visible wavelength-excitable polymethine cyanine dye Cy3 (lambda(max) abs = 556 nm; lambda(max) em = 567 nm) to several single-cysteine variants of maltose binding protein (MBP), followed by evaluation of each of these labeled proteins as potential reagentless sensors for maltose. Four of six MBP variants labeled with the Cy3 probe functioned successfully in a homogenous reagentless sensing mode, and yielded maltose dissociation constants ranging from 74 muM to 3.8 mM. Cy3 and other cyanine dye derivatives may be useful as long-wavelength excitable reporter groups in other reagentless sensor designs.