Hi Christian, Here are the rules for atom names in correct PDB format, as I understand them: Atom names start with element symbols right-justified in columns 13-14 as permitted by the length of the name. For example, the symbol FE for iron appears in columns 13-14, whereas the symbol C for carbon appears in column 14. If an atom name has four characters, however, it must start in column 13 even if the element symbol is a single character (for example, some hydrogens). So while it is true that columns 13-16 are for atom names, just putting the names anywhere in that area does not mean the format is correct. The Chimera User's Guide includes some information on PDB format: <http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/tutorials/framepdbintro.html
I hope this helps, ELaine ----- 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 On Mar 17, 2009, at 6:57 AM, Christian Schudoma wrote:
Hello Chimera-Users and -Devs, I encountered the following problem when trying to visualise the following purine molecule (Actually, I tried to do something more complex(*) but the same problem can be reproduced with this more simple example). For clarification, the first lines contain the column numbers.
1 2 3 4 5 6 7 123456789012345678901234567890123456789012345678901234567890123456789012345678 HETATM 1 N1 CKN A 1 -0.003 1.586 -3.371 0.00 0.00 N HETATM 2 C2 CKN A 1 1.016 1.511 -4.278 0.00 0.00 C HETATM 3 N3 CKN A 1 2.313 1.566 -3.865 0.00 0.00 N HETATM 4 C4 CKN A 1 2.576 1.683 -2.541 0.00 0.00 C HETATM 5 C5 CKN A 1 1.559 1.758 -1.597 0.00 0.00 C HETATM 6 C6 CKN A 1 0.224 1.717 -2.032 0.00 0.00 C HETATM 7 N7 CKN A 1 2.100 1.858 -0.373 0.00 0.00 N HETATM 8 C8 CKN A 1 3.434 1.842 -0.568 0.00 0.00 C HETATM 9 N9 CKN A 1 3.731 1.742 -1.876 0.00 0.00 N
When I load a pdb file containing these coordinates into Chimera, I get 9 non-connected dots (obviously representing the atoms) which can neither be coloured by hetero-atom, nor by element. Note that the atom names are located in the appropriate columns, i.e. between columns 13 and 16, more specifically in columns 15 and 16.
I noticed that in other pdb structures 2-character atom names are located in columns 14 and 15 and when I put my atom names there, Chimera displays the purine ring system which then can be coloured by hetero-atom/element. Now it is nice that this workaround fixes my problem, however, according to the pdb file format specification (columns 13-16 are reserved for the atom name), atom names located in columns 15 and 16 are valid(*) and as such should be processible by visualisation tools etc.
The behaviour occurs with the latest daily build as well as some older versions I found on my hard disk...
(*) The purine is part of a larger cytokinin. I stumbled upon the described behaviour while using the AddHydrogen function on the whole molecule, which lead to the replacement of the purine with a hydrogen. (**) Unless there are some additional rules regarding the placement of atom names shorter than 4 characters, in which case I apologise for bugging you with this.
Any comments on this?
Best regards, Christian Schudoma