title: Detection of local polarity of alpha-lactalbumin by N-terminal specific labeling with a new tailor-made fluorescent probe.
abstract: To detect the local polarity such as the N-terminal domain of a protein molecule, 3-(4-chloro-6-hydrazino-1,3,5-triazinylamino)-7-(dimethylamino)-2-methylphenazine has been designed and synthesized as a polarity-sensitive fluorescent probe by using an s-triazine ring as a backbone, neutral red and hydrazine as a polarity-sensitive fluorophore, and a labeling group, respectively. The fluorescence properties of the probe have been characterized. The probe has the following features: (1) stable in various solvents; (2) the long-wavelength emission of >550 nm that can avoid the interferences of the background fluorescence shorter than 500 nm from common biomacromolecules; and (3) the maximum emission wavelength (lambda(em)) sensitive to solvent polarity only but not to pH and temperature. The hydrazino group in such a probe reacts readily with an active carbonyl produced by transamination of a protein molecule, leading to N-terminal specific attachment of the fluorophore and thereby allowing the monitoring of local polarity. With this probe, the polarity of the N-terminal domain in both native and heat-denatured alpha-lactalbumin has been first determined, which corresponds to that with a dielectric constant of about 16, and the hydrophobic core near the N-terminus is found to be conservative for heating. The present strategy may provide a general method to study the local environmental changes of a protein molecule under different denaturation conditions.
authors.affiliation: Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China.
authors.forename: Su-Ying
authors.initials: SY
authors.lastname: Dong
authors.forename: Hui-Min
authors.initials: HM
authors.lastname: Ma
authors.forename: Xue-Jun
authors.initials: XJ
authors.lastname: Duan
authors.forename: Xin-Qi
authors.initials: XQ
authors.lastname: Chen
authors.forename: Jun
authors.initials: J
authors.lastname: Li
mesh_terms: D005456:Fluorescent Dyes / Q000138:chemical synthesis*; D006358:Hot Temperature; D007768:Lactalbumin / Q000737:chemistry*; D010619:Phenazines / Q000138:chemical synthesis; D011489:Protein Denaturation; D055672:Static Electricity
chemical_list: D005456:Fluorescent Dyes; D010619:Phenazines; D007768:Lactalbumin