Dear Jaya, (1) Chimera will display whatever coordinates and residue names are present in the input file. It does not matter if the residues or the atoms in them are standard or not. However, you cannot define new residues to be built by Chimera with the "swapaa" or "addaa" commands. We have recently added a Build Structure tool (Structure Editing category) that lets you add arbitrary atoms and bonds to structures interactively. It is in the early stages of development, however, and is likely to change in the future. If you use this, you may want to check the bond lengths and adjust them in the "Set Bond Length" section of the Build Structure tool. The man page for Build Structure: http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/editing/ editing.html (2) Chimera does not do any automated docking. However, you can manually/interactively dock structures by moving one relative to the other (to freeze a structure and move only the others, you would uncheck its Active button in the Model Panel or its checkbox under the Command Line). The man page for the Model Panel: http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/modelpanel.html (3) I believe there is no limit on the number of amino acids present in the protein. There may be limitations due to the input file format (that is, the residue number column can only be a certain width in the input file format, usually PDB). However, in combination with use of different chain IDs this limit is quite high. For example, ribosome structures can be viewed in Chimera, although it may take a while for the structure to load. I hope this helps, Elaine On Jun 23, 2006, at 8:06 AM, Jaya Bhatnagar wrote:

Hi, Is it possible in chimera to define a new amino acid residue? Also, what algorithms does it support involving docking of two proteins? And is there a limit on number of amino acids present in the protein?

thanks a lot, Jaya

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----- Elaine C. Meng, Ph.D. meng@cgl.ucsf.edu UCSF Computer Graphics Lab and Babbitt Lab Department of Pharmaceutical Chemistry University of California, San Francisco http://www.cgl.ucsf.edu/home/meng/index.html