Auto-creation of bonds.

[BradyAJohnston]

I'm sorry if this is obvious, but I have looked around and tried to have a go at it myself, but I am unable to find a way to "auto" generate bonds from a pdb, based on proximity to other atoms etc. Is this implemented somewhere by any chance?

I am currently testing out & implementing atomium for use inside of blender which has enabled me to import pdb files which I couldn't do previously. Any extra information that I can squeeze out of this library would be a great help with not having to reimplement it myself!

[samirelanduk]

Hi - currently no, and it's probably the biggest gap in functionality. I'm currently close to finishing a 2.0 version of atomium, and overhauling the bond generation is vaguely planned for 2.1, though it's hard to say when that will be. I would like to implement something like the PyMol system where the user can generate bonds based on a variety of rules and cutoffs.

Glad it's useful nonetheless - let me know if there's anything else I can help with, and I'll leave this issue open to be closed during the planned 2.1 release.

(Those animations look incredible by the way.)

[BradyAJohnston]

Thanks! Atomium is crucial to making it all work smoothly, so thank you for developing the package!

The addon is now released into beta and so far atomium has been working flawlessly for importing and handling the structures: https://github.com/BradyAJohnston/MolecularNodes

In terms of a list of features that I would want after working with it so far (I am working with the pip release so unaware of any updated features in the dev branch):

• Atoms to be aware of their residue, like the atom.chain but atom.residue
• Atoms to have a variety of radii available (covalent, VDW etc)
• Bond generation in the structure
• Residues to have a property that is just their number in the sequence / chain "9" rather than "A.9"
• Abilitiy to get an ordered list of the residues or atoms from model.atoms() etc, at the moment I have to get the atom IDs and then reorder the list based on this, so that is consistent across models in a multi-model PDB file.

[BradyAJohnston]

I implemented my own bond-generation code. I had to include my own dictionary for looking up Van der Waal's radii. If you have any idea for improvements I'd be interested in the meantime as well!

radii_dict = {
    "H"  : 1.10, 
    "He" : 1.40, 
    "Li" : 1.82, 
    "Be" : 1.53, 
    "B"  : 1.92, 
    "C"  : 1.70, 
    "N"  : 1.55, 
    "O"  : 1.52, 
    "F"  : 1.47, 
    "Ne" : 1.54, 
    "Na" : 2.27, 
    "Mg" : 1.73, 
    "Al" : 1.84, 
    "Si" : 2.10, 
    "P"  : 1.80, 
    "S"  : 1.80, 
    "Cl" : 1.75, 
    "Ar" : 1.88, 
    "K"  : 2.75, 
    "Ca" : 2.31, 
    "Sc" : 2.11, 

    # break in the elements, no longer in direct numerical order
    "Ni" : 1.63, 
    "Cu" : 1.40, 
    "Zn" : 1.39
}

def create_bonds(model, connect_cutoff = 0.35, search_distance = 3):
    """
    # from the pymol wiki: https://pymolwiki.org/index.php/Connect_cutoff
    # connect_cutoff = 0.35
    # Two atoms with VDW radii vdw1 and vdw2 are connected with a bond, if the following inequality is true:
    # distance <= connect_cutoff + (vdw1 + vdw2)/2
    """
    for atom in model.atoms():
        primary_atom = atom
        primary_radius = radii_dict[atom.element]
        nearby_atoms = atom.nearby_atoms(search_distance)

        for secondary_atom in nearby_atoms:
            if atom.element == "H":
                connect_adjust = -0.2
            elif secondary_atom.element == "S" & atom.element == "S":
                connect_adjust = 0.2
            else:
                connect_adjust = 0

            secondary_radius = radii_dict[secondary_atom.element]
            distance = atom.distance_to(secondary_atom)
            if distance <= ((connect_cutoff + connect_adjust) + (primary_radius + secondary_radius) / 2):
                primary_atom.bond(secondary_atom)

[samirelanduk]

Of your suggestions, 1 and 4 are already implemented in 2.0, so hopefully that should be available on PyPI soon. 2 would definitely be useful, and easy to implement. 3 as we discussed is definitely planned. 5 is interesting - I comitted to have them be sets a long time ago because I thought 'well they're just in 3D space, they don't really have an order, unlike residues in a chain' - but to be honest, them being unordered annoys me a lot too when I use atomium. Need to think about this a bit more.

Code looks great. I think it would be worth me adding an option to distance_to to just return the square of the distance, which is computationally easier to calculate and if you're just checking if the distance is below some threshold, you can just compare the square of the distance to the threshold.

[BradyAJohnston]

Yeah I can understand the approach, and it I initially though it wouldn't be an issue, but in a multi-state / multi-model PDB file, the same atoms across two different structures end up at different positions in the set. An option to return an ordered list instead of a set, but still have the set as a default maybe would be a good approach.

[BradyAJohnston]

Another item for my wishlist would be access to the space group / crystal symmetry / unit cell from a .pdb file when opened.

[samirelanduk]

Also planned for 2.0! In the mean time you can do:

import atomium
pdb = atomium.open("myfile.pdb", file_dict=True)
crystal_record = pdb["CRYST1"]

...to get the relevant record. Still needs splitting etc though.

[BradyAJohnston]

Ah excellent, thank you!

[BradyAJohnston]

Is there a planned ETA for atomium 2.0? I'm thinking about making some changes to Molecular Nodes internals that would be made easier by the changes planned for 2.0.

[samirelanduk]

Unfortunately it's likely to be several months - I am completely consumed by my main work at the moment. :/

[BradyAJohnston]

Completely understand! Might take a look at some of it in a few months myself but I think everyone is pretty busy these days