|Monoclonal Antibody to Human Topoisomerase I Covalent Complexes (Top1-CC)|
|TG2017-1||100 Units||$225.00||Order Now|
|TG2017-2||250 Units||$345.00||Order Now|
Topoisomerases engage DNA in two ways: either as conventional DNA binding proteins (weak binding) or in cleavage complexes (covalent complexes). Weak binding is mediated by ionic bonding or electrostatic forces are is sometimes referred to as a 1-D or 3-D scanning process, wherein the enzyme is searching (scanning) the DNA to locate an optimal binding site. Optimal binding may be sequence dependent to some extent but not always. Topoisomerases have the unique ability to respond to topological features as well (like twist and writhe or helical tension). This weak binding/scanning is followed by DNA cleavage, once the enzyme finds a suitable site. Since the cleavage is a transesterification, the energy in the phosphodiester backbone is conserved through the formation of a transient covalent bond with DNA (a phosph-tyrosyl link). These covalent complexes are exceptionally difficult to see since the complex is so fleeting. However, interfacial poisons, such as camptothecin may intervene, increasing the half-life of the covalent complex and making it possible to detect their presence (using procedures such as the ICE Assay). These complexes are directly responsible for cytotoxicity (and tumor cell death). Therefore, the availability of a specific antibody that detects only Top1 that is bound in a covalent complex, is an extremely useful reagent. It can be used as a predictive biomarker, for example (Patel, et al, 201).
We compared an ICE blot using two distinct monoclonal antibody probes (Fig. 1). It is clear that the Top1-CC gives very clear results compared to an antibody directed against intact 100kDa Top1 (unbound).
Patel, A.,et al 2016. Immunodetection of human topoisomerase I-DNA covalent complexes. Nuc. Acid. Res. 44: 2816–2826
The antibody is shipped on blue ice. It is stable for 1-2 months at 4°C and for long term storage should be kept frozen. Repeat freeze/thawing is deleterious and should be minimized.