3.PDB:

PDB is a protein data bank it contains information about the structure and function of the reported proteins. Not only the information about the protein is present but also of many macromolecules like nucleic acids and carbohydrates.
How to Search PDB:
go to http://www.rcsb.org/pdb/explore/motm.do
enter PDB ID if you don't know the ID then enter the text methylenetetrahydrofolate reductase to get the structural information of that protein
I entered this text then get this result go to this page http://www.rcsb.org/pdb/results/results.do?outformat=&qrid=FA02BFE5&tabtoshow=Current