# How to interpret the affinity in a protein docking - ligand

I'm performing a molecular docking using a trans-membrane protein and several ligands.

For the first ligand, the best conformation gave a binding energy of 110 kcal/mole, being 50 kcal/mole the binding energy for the second conformation.

However, these values ​​have no meaning without a frame of reference. Is there a basic rule of thumb to keep in mind to know if our results seem consistent and is it worth further investigation?

This question also arises as I remember watching a tutorial where the binding energy was of -5 (?), but then again I don´t remember the units for this docking.

The score functions are designed in order to take into account different interactions types between the ligand and the protein. These interactions include electrostatic, hydrophobic, hydrophilic, and hydrogen interactions, for example. They can also be designed using a set of experimental binding data ($$IC_{50}$$, inhibition constant -$$k_i$$-, for example). The X-SCORE function is one that include three empirical scoring functions.