[Chimera-users] making capsid map from asymmetry unit.

[Elaine Meng]

Hi Jian,
Sorry this is a rather long answer, because I ran into several issues…

In general, you could 
(1) build multimer atomic structure of capsid based on symmetry information in the PDB file, using Multiscale Models tool or command "sym" (e.g.: sym #0)<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/sym.html>
(2) simulate density map from atomic structure with command "molmap"  (e.g.: molmap #  10) … where 10 is adjustable parameter, see the manual
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/molmap.html>

However, for 3iyi specifically I see that the atomic structure is only the CA backbone.  The process above would still make something that looked like a map, but   the "densities" would be nonquantitatively low and you would have to contour at very low level to make it look reasonable.  

>From the page for 3iyi at the PDB, I see the structure is from cryoelectron microscopy (cryoEM) in the first place, so I thought it might make more sense just to get the cryoEM map from EMDB, if available.  
<http://www.rcsb.org/pdb/explore/explore.do?structureId=3iyi>

To find out EMDB ID numbers, I looked at the (open access) citation given in that PDB page:

P22 coat protein structures reveal a novel mechanism for capsid maturation: stability without auxiliary proteins or chemical crosslinks.
Parent KN, Khayat R, Tu LH, Suhanovsky MM, Cortines JR, Teschke CM, Johnson JE, Baker TS.
Structure. 2010 Mar 10;18(3):390-401
<http://www.sciencedirect.com/science/article/pii/S0969212610000328>

… which gives accession numbers EMD-4159 (for "ExH particles," you would need to read the paper for explanation) and EMD-4150.  In Chimera you can fetch EMDB entries with menu: File… Fetch by ID, database: EMDB, or command, e.g.: open emdbID:4159

Unfortunately, I see that those entries are not found!!!  I don't know why.  I also could not find them at the EMDB website.

So, my only idea to get a map is the 2-step process above.

Or, without making a map, you can show the capsid with each subunit as a "blob" using Multiscale Models (in menu under Tools… Higher-Order Structure).  The images at the PDB are similar to that:
<http://www.rcsb.org/pdb/explore/images.do?structureId=3IYI>

I hope this helps,
Elaine
----------
Elaine C. Meng, Ph.D. 
UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab
Department of Pharmaceutical Chemistry
University of California, San Francisco

On Jun 24, 2014, at 7:49 AM, "Jian Guan" <jug25 at psu.edu> wrote:

> Dear All,
> I want to make a capsid map from asymmetry unit. The PDB ID is 3iyj, the L1 protein of BPV. The BPV is a T=7, icosahedral capsid. Does anybody know how to make it? Thanks a lot.
> Sincerely yours,
> Jian