Science is based upon incremental advances of previous work. A year ago, Dan blogged about worked on BioA. The key take home from that work was that a hydrazine fragment ended up destabilizing the target by 18C. It ended up being, as expected, a reversible, SAM-competitive inhibitor with modest potency. As Dan concluded:
This is a very nice paper, and it will be fascinating to try to understand how the fragments so effectively destabilize the protein despite binding tightly, and how this translates into inhibition. The researchers suggest that finding ligands that destabilize proteins could be generally useful for turning off proteins.
In this paper, the same group is back (This work was also presented at DDC in San Diego in April). Interestingly, they seemed to have abandoned the hydrazine. Taking the same approach (DSF-Xray-ITC) they identify different fragments (2% hit rate from a 1000 screened). 9 were stabilizers (average of +3.8C) and 12 were destabilizers (average of -13.8C(!)). 5 fragments were able to be crystallized by soaking, co-crystallization was able to add one more structure (Figure 1). Interestingly, the calorimetry showed that only F5's binding is strongly, enthalpically driven.
|Figure 1. Crystallographically Confirmed Fragment Hits|
- Little correlation between magnitude of Tm shift and confirmation by crystallization
- Stabilizing and destabilizing compounds were confirmed by Xray
- No correlation between magnitude of the Tm shift and calorimetry determined Kd.
- Conformational flexibility in the target active site need to be taken into account.