Do conjugated toxins (dermorphin-saporin in particular) exhibit agonist effects? I’ve generated behavioral and tissue time course effects but have not established agonist effects for this conjugated toxin.
The peptide ligand toxins should exhibit agonist effects. They are constructed purposely to retain complete agonist activity, including for us the most important: internalization. So, for instance, SP-SAP (Cat. #IT-07) causes receptor internalization similar to SP, as reported in Mantyh et al. (Inhibition of hyperalgesia by ablation of lamina I spinal neurons expressing the substance P receptor. Science 278:275-279, 1997).
As to dermorphin-SAP (Cat. #IT-12) specifically, it has agonist activity very much like dermorphin. This is reported in Porreca et al. (Inhibition of neuropathic pain by selective ablation of brainstem medullary cells expressing the mu-opioid receptor. J Neurosci 21:5281-5288, 2001) in which it’s stated:
The bilateral microinjection of 3 pmol of dermorphin or of dermorphin-saporin directly into the RVM produced a robust antinociceptive effect in the 52°C hot-water tail-flick test. The peak antinociceptive effect of dermorphin, 78 ± 13.2% MPE, was not significantly different from that of the dermorphin-saporin conjugate, which was 59 ± 4.7% MPE (p > 0.5, Student’s t test).
Usually the amount needed to give a response is lower than the amount needed to kill a cell. Depending on what your system is; it may be a peculiarity of that system, but I would be a little concerned about not seeing an agonist effect. On the other hand, if you have demonstration of specific toxicity, it may not be all that crucial.
See also: Targeted Toxins Catalog