An efficient method for conjugation of thiamine to proteins

High-Throughput Detection of Thiamine Using Periplasmic Binding Protein-Based Biorecognition

Although antibodies and aptamers are commonly used bioaffinity recognition elements, they are not available for many important analytes. As an alternative, we demonstrate use of a periplasmic binding protein (PBP) to provide high affinity recognition for thiamine (vitamin B1), an analyte of great importance to human and environmental health for which, like so many other small molecules, no suitable biorecognition element is available. We demonstrate that with an appropriate competitive strategy, a highly sensitive (limit of detection of 0.5 nM) and specific bioassay for thiamine and its phosphorylated derivatives can be designed. The high-throughput method relies upon the thiamine periplasmic binding protein (TBP) from Escherichia coli for thiamine biorecognition and dye-encapsulating liposomes for signal-enhancement. A thiamine monosuccinate-PEG-biotin derivative was synthesized to serve as an immobilized competitor that overcame constraints imposed by the deep binding cleft and structural recognition requirements of PBPs. The assay was applied to ambient environmental samples with high reproducibility. These findings demonstrate that PBPs can serve as highly specific and sensitive affinity recognition elements in bioanalytical assay formats, thereby opening up the field of affinity sensors to a new range of analytes.

Specific association of thiamine-coated gadolinium nanoparticles with human breast cancer cells expressing thiamine transporters

Thiamine (vitamin B(1)) was investigated as a tumor-specific ligand for gadolinium nanoparticles. Solid nanoparticles containing gadolinium hexanedione (1.5 mg/mL) were engineered from oil-in-water microemulsion templates and coated with thiamine ligands. Thiamine ligands were synthesized by conjugating thiamine to either distearoylphosphatidylethanolamine (DSPE) or fluorescein via a poly(ethylene glycol) (PEG) spacer (Mw 3350). The efficiency of thiamine ligand attachment to nanoparticles was evaluated using gel permeation chromatography (GPC). Cell association studies were carried using a methotrexate-resistant breast cancer cell line, MTX(R)ZR75, transfected with thiamine transporter genes (THTR1 and THTR2). Thiamine-coated nanoparticle association with THTR1 and THTR2 cells was significantly greater than that with control breast cancer cells (MTX(R)ZR75 transfected with the empty expression vector pREP4) (p < 0.01; t-test). The nanoparticle cell association was significantly dependent on the extent of thiamine ligand coating on nanoparticles, expression of thiamine transporters in cells, temperature of incubation, and the concentration of competitive inhibitor (free thiamine). Further studies are warranted to assess the potential of the engineered thiamine-coated gadolinium (Gd) nanoparticles in neutron capture therapy of tumors.