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A study involved the measurement of the kinematic values of attractant binding of the ligand region of chemotaxis aspartate receptor. The structural regions involved in attractant-induced conformational change were located. Each subunit of the homodimer revealed six parafluorophenylalanine (4-F-Phe) positions. The dissociation rate constant (k-off approximately equal to 10 cubed per second) was calculated from the association rate constant (K-on approximately equal to 10 to the 9th power meter per second) of the bond between the isolated periplasmic domain and the aspartate.

An analysis of structural, chemical and cooperative properties of Escherichia coli and Salmonella typhimurium aspartate receptors reveals that both have specific negatively cooperative binding configurations. Amino acid sequences for aspartate receptors have 79% identity but the E. coli receptor exhibits single site binding. Consequently, the E. coli receptor binds with 'half-of-the sites' cooperativity, where the E. coli receptor's second ligand does not bind.

Two of the three components of anthrax toxin, protective antigen (PA) and lethal factor (LF), together known as lethal toxin (LeTx), reportedly show anti-tumor activity in melanoma in vitro and in vivo. The growth inhibitory activity of LeTx in culture was determined in nine human cancer cell lines, including melanoma, neuroblastoma and adenocarcinoma cells, as well as in human umbilical vein endothelial cells (HUVEC). The contribution of the two known PA receptor proteins, ANTXR1/TEM8 and ANTXR2/CMG2, to the sensitivity of the cells was assessed. The efficacy of LeTx was evaluated in vivo in the SK-N-AS neuroblastoma and SK-MEL-28 melanoma tumor xenograft models. Sensitivity to LeTx in vitro was observed in the neuroblastoma and colorectal adenocarcinoma cells and HUVEC, as well as melanoma cells. ANTXR1/TEM8 and ANTXR2/CMG2 protein expression studies suggested that a certain threshold of the PA receptor protein level must be met for sensitivity to LeTx to be observed. However, although the SK-N-AS neuroblastoma cells expressed the highest levels of receptor proteins and achieved the lowest IC50 in vitro (0.1 ng/ml), we observed no correlation between either the ANTXR1/TEM8 or ANTXR2/CMG2 protein levels and sensitivity to LeTx in vitro. In vivo, LeTx was an active anti-tumor agent when administered intravenously to mice bearing the human SK-N-AS or SK-MEL-28 tumor xenografts. The tumor growth delays were 6-8 days with a lower dose regimen and 14-16 days with a higher dose regimen for the two tumor models. These in vitro data suggest that LeTx may have broad therapeutic indications in cancer and the in vivo studies demonstrate that LeTx has systemic efficacy in neuroblastoma as well as melanoma. The therapeutic potential of LeTx needs to be further investigated in non-melanoma tumor models expressing the ANTXR1/TEM8 and/or ANTXR2/CMG2 protein.