we now have.

All major scientific subjects are almost equally but all intensively involved:

Chemistry:
crystal growing, heavy metal ions, cross linking and other modification

Physics:
microgravity nucleation of crystals, diffraction by crystals, synchrotron radiation, thermodynamics of protein folding

Mathematics:
phasing, crystal packing

Computer science:
phasing, programming, structure prediction, informatics, etc

Molecular Biology:
cloning, protein expression and purification, genomics, etc.

And finally, Medicine.

A protein crystasllographer is not easy.