Does anyone know how to 3D-print protein structures?
The best you can do is do gene synthesis using a method called Oligonucleotide Synthesis
http://en.wikipedia.org/wiki/Oligonucleotide_synthesis
Using this technique, you can take an arbitrary gene sequence (ATGC sequence) and get a plasmid out of it. This will specify a sequence of amino acids that will fold into a protein. Then you just have to get a bacterial host to take it up into it's DNA and then make sure the chemical conditions of the host are right to generate your protein (you can't synthesize a protein if there aren't the right types of Amino Acids floating around, for example).
Companies like Genscript (which I found by randomly googling) will manufacture a specified gene, and send you back frozen plasmids, which you can then inject into your favorite bacterial host.