In order to identify
the locations of metal ions in the
binding
sites of proteins, we have developed a method named the MADE (MAcromolecular
DEnsity and Structure Analysis) approach. The MADE approach represents
an evolution of our previous toolset, the ProBiS H2O (MD)
methodology, for the identification of conserved water molecules.
Our method uses experimental structures of proteins homologous to
a query, which are subsequently superimposed upon it. Areas with a
particular species present in a similar location among many homologous
protein structures are identified using a clustering algorithm. Dense
clusters likely represent positions containing species important to
the query protein structure or function. We analyze well-characterized apo protein structures and show that the MADE approach can
identify clusters corresponding to the expected positions of metal
ions in their binding sites. The greatest advantage of our method
lies in its generality. It can in principle be applied to any species
found in protein records; it is not only limited to metal ions. We
additionally demonstrate that the MADE approach can be successfully
applied to predict the location of cofactors in computer-modeled structures,
e.g., via AlphaFold. We also conduct a careful protein superposition
method comparison and find our methodology robust and the results
largely independent of the selected protein superposition algorithm.
We postulate that with increasing structural data availability, additional
applications of the MADE approach will be possible such as non-protein
systems, water network identification, protein binding site elaboration,
and analysis of binding events, all in a dynamic manner. We have implemented
the MADE approach as a plugin for the PyMOL molecular visualization
tool. The MADE plugin is available free of charge at .