Solved it using Maestro. Import the .pdb file, select "Periodicity" and under "Show Atoms" select "All Atoms". Export as a .pdb file. But it makes a few strange long-bonds better the crystallised water molecules, this can be seen in VMD after loading in the new structure. Also, using "pdb box_draw" in the VMD terminal window will show the unit cell dimensions, and then just use "periodicity" under "Graphical Representation" to visualise the supramolecular structure. 

Also note that this kind of construction is very simple to do in CHARMM (or online via CHARMM-GUI).

"online via CHARMM-GUI"

Thanks, Justin, I didn't know that. 

Sadly, I spoke too soon. Although Maestro will display the protein lattice in the unitcell (just as NGL viewer in the PDB website will), by exporting as a .pdb all identical atoms type from each identical residue e.g., CA in Res1 of protein A/B/C/D are listed together e.g., CA,CA,CA,CA for Res 1 of protein 1, 2, 3, 4, followed by C, C, C, C for Res 1 of protein 1, 2, 3, 4. e.g.,

ATOM      1  N   GLY B  33       3.470   0.200   4.525  0.60 16.89           N

ATOM      2  N   GLY B  33     166.104   0.200  20.376  0.60 16.89           N

ATOM      3  N   GLY B  33      89.257   7.170   4.525  0.60 16.89           N

ATOM      4  N   GLY B  33      80.317   7.170  20.376  0.60 16.89           N

ATOM      5  N   GLY B  33       3.470  14.139   4.525  0.60 16.89           N

ATOM      6  N   GLY B  33     166.104  14.139  20.376  0.60 16.89           N

ATOM      7  CA  GLY B  33       4.136   1.541   4.532  0.60 15.15           C

ATOM      8  CA  GLY B  33     165.438   1.541  20.369  0.60 15.15           C

ATOM      9  CA  GLY B  33      89.923   8.511   4.532  0.60 15.15           C

ATOM     10  CA  GLY B  33      79.651   8.511  20.369  0.60 15.15           C

ATOM     11  CA  GLY B  33       4.136  15.480   4.532  0.60 15.15           C

ATOM     12  CA  GLY B  33     165.438  15.480  20.369  0.60 15.15           C

I might try the oneline CHARMM-GUI.

Could you solve it? I don't know how to calculate the correct dimensions for the unit cell box.