Hi Elaine, BD simulations is brownian dynamics. Well my file is in a PDB format, and basically consist of a single complex, with heteroatoms living from one active site to the other. If you open the file as a pdb file you will realized the heteroatoms HOH are static. But I want them to be able to move from the active site of one enzyme to the other in the complex.

I was thinking that I can put the word Model, between the complex, and each heteroatom HOH, so as to make the file seem to have many pdb files.

Hi Neville, Yeah, I eventually realized you meant Brownian dynamics! But what matters for Chimera is the format rather than how the trajectory was generated. To use "MD Movie" to play/record the trajectory, your PDB format options are: (a) put each frame in a separate PDB file The file names must include frame numbers, and files for all intermediate frames must also be present. The files must not contain END records. (b) put all the frames in one PDB file, but bracket each with MODEL and ENDMDL, as is done for NMR ensembles in the Protein Databank, e.g. 1g1p. The MODEL numbers are interpreted as frame numbers and should start with 1 or 0 and increment by 1. Either way, atom names, residue names/numbers need to be the same between frames. ** In general, each frame should have the same number of atoms. However, for "weird" cases where lots of atoms stay in the same position (which if I understand correctly is what you have), we have made a special provision: if the coordinates supplied for a frame represent only a subset of the atoms in the preceding frame, it will be inferred that the remaining atoms are present but have the same coordinates as in the preceding frame. Changes are cumulated in the forward direction and based on all frames, even when frames are skipped during playback. All of the atoms must be in the first frame, of course. In your case, I guess that would include the proteins plus the starting locations of the heteroatoms. You might need to renumber the HOHs to keep their identities across the frames... looks like what you sent gives each position a different residue number. This information as well as how to play the trajectory and record it as a movie are in the MD Movie manual page (choose Help... User's Guide, click Tools tab, click link "MD Movie"). I hope this helps, Elaine ----- Elaine C. Meng, Ph.D. meng@cgl.ucsf.edu UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab Department of Pharmaceutical Chemistry University of California, San Francisco http://www.cgl.ucsf.edu/home/meng/index.html