We developed an on-chip activity assay system to simultaneously determine the transamidating activities of
blood coagulation factor XIII (FXIII) and
transglutaminase 2 (TG2) by use of
fibrinogen arrays. FXIII and TG2 are
transglutaminase family members that are involved in various physiological functions, including vascular pathophysiology, bone development, and
cancer progression. However, investigation of their differential functions is limited by the lack of high-throughput and
isozyme-specific activity assays. For the on-chip activity assay, we fabricated
protein arrays by immobilizing
fibrinogen onto the
3-aminopropyltrimethoxysilane surface of well-type arrays, and we determined transamidating activity by probing biotinylated
fibrinogen with Cy3-conjugated
streptavidin on arrays. We optimized assay conditions, such as
buffer pH, concentrations of
dithiothreitol and
5-(biotinamido)pentylamine, and incubation time, and we created equations to determine specific FXIII and TG2 activities in samples. We successfully applied this assay system to monitor changes in FXIII and TG2 activities in THP-1 monocytic cells differentiated with
phorbol 12-myristate13-acetate and
interleukin-4. This activity assay is sensitive and suitable for high-throughput determination of FXIII and TG2 activities and thus has a strong potential for investigating the differential functions of these
isozymes in cell signaling and cardiovascular pathophysiology research.