Atomic and molecular properties

Some simple atom properties can be retrieved using special functions, which operate on atoms of the type Atom. For example:

julia> atoms = read_pdb("./file.pdb");

julia> printatom(atoms[1])
   index name resname chain   resnum  residue        x        y        z  beta occup model segname index_pdb
       1   OW     SOL     X        1        1   54.370   45.310   33.970  0.00  0.00     1       -         1

julia> mass(atoms[1])
14.0067

julia> atomic_number(atoms[1])
7

julia> element(atoms[1])
"N"

julia> element_name(atoms[1])
"Nitrogen"

The formula or stoichiometry of a selection can also be retrieved:

julia> atoms = wget("1LBD","protein and residue 1");

julia> f = formula(atoms)
C₃N₁O₂

julia> stoichiometry(select(atoms,"water"))
H₂O₁

PDBTools.mass — Function

mass(s::Sequence)

Returns the mass of a sequence of amino acids, given a Sequence struct type.

Examples

julia> seq = ["Alanine", "Glutamic acid", "Glycine"];

julia> mass(Sequence(seq))
257.2432

julia> seq = "AEG";

julia> mass(Sequence(seq))
257.2432

julia> seq = ["ALA", "GLU", "GLY"];

julia> mass(Sequence(seq))
257.2432

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mass(atom::Atom)
mass(atoms::AbstractVector{<:Atoms})

Returns the mass of an atom given its name, or Atom structure, or the total mass of a vector of Atoms.

If a mass is defined as a custom field in the the Atom structure, it is returned. Otherwise, the mass is retrieved from the element mass as inferred from the atom name.

Example

julia> using PDBTools

julia> atoms = [ Atom(name="NT3"), Atom(name="CA") ];

julia> mass(atoms[1])
14.0067

julia> mass(atoms)
26.017699999999998

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PDBTools.element — Function

element(atom::Atom)

Returns the element symbol, as a string, of an atom given the Atom structure. If the pdb_element is empty or "X", the element is inferred from the atom name. Othwerwise, the pdb_element is returned.

Example

julia> using PDBTools

julia> at = Atom(name="NT3");

julia> element(at)
"N"

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PDBTools.element_name — Function

element_name(atom::Atom)

Returns the element name of an atom given its name, or Atom structure.

Example

julia> using PDBTools

julia> at = Atom(name="NT3");

julia> element_name(at)
"Nitrogen"

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PDBTools.element_symbol — Function

element_symbol(atom::Atom)

Returns a symbol for element name of an atom given its name, or Atom structure.

Example

julia> using PDBTools 

julia> at = Atom(name="NT3");

julia> element_symbol(at)
:N

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PDBTools.element_symbol_string — Function

element_symbol_string(atom::Atom)

Returns a string with the symbol of the element, given the Atom structure.

Example

julia> using PDBTools 

julia> at = Atom(name="NT3");

julia> element_symbol_string(at)
"N"

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PDBTools.formula — Function

formula(atoms::AbstractVector{<:Atom})

Returns the molecular formula of the current selection.

Example

julia> using PDBTools

julia> pdb  = read_pdb(PDBTools.TESTPDB, "residue 1"); # testing PDB file

julia> resname(pdb[1])
"ALA"

julia> formula(pdb)
H₇C₃N₁O₁

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PDBTools.stoichiometry — Function

stoichiometry(atoms::AbstractVector{<:Atom})

Returns the stoichiometry of atom selection in a Formula structure.

Example

julia> using PDBTools

julia> pdb  = read_pdb(PDBTools.TESTPDB, "water"); # testing PDB file

julia> stoichiometry(pdb)
H₂O₁

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PDBTools.printatom — Function

printatom(atom::Atom)

Prints an Atom structure in a human-readable format, with a title line.

Example

julia> using PDBTools

julia> atoms = read_pdb(PDBTools.TESTPDB, "protein and residue 2");

julia> printatom(atoms[1])
   index name resname chain   resnum  residue        x        y        z occup  beta model segname index_pdb
      13    N     CYS     A        2        2   -6.351  -14.461   -5.695  1.00  0.00     1    PROT        13

julia> atoms[1] # default show method
      13    N     CYS     A        2        2   -6.351  -14.461   -5.695  1.00  0.00     1    PROT        13

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AtomsBase compatibility

The following functions are supported as part of the API, to conform the AtomsBase interface:

Function	Example	Output
`atomic_number(::PDBTools.Atom)`	`atomic_number(Atom(name="NE2"))`	`7`
`atomic_symbol(::PDBTools.Atom)`	`atomic_symbol(Atom(name="NE2"))`	`:N`
`atomic_mass(::PDBTools.Atom)`	`atomic_mass(Atom(name="NE2"))`	`14.0067`
`position(::PDBTools.Atom)`	`position(Atom(name="NE2"))`	`SVector{3,Float64}(0,0,0)`

AtomsBase.atomic_number — Function

atomic_number(atom::Atom)

Returns the atomic number of an atom from its Atom structure.

Example

julia> using PDBTools

julia> at = Atom(name="NT3");

julia> atomic_number(at)
7

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AtomsBase.atomic_symbol — Function

atomic_symbol(atom::Atom)

Returns the atomic symbol of an atom given the Atom structure.

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AtomsBase.atomic_mass — Function

atomic_mass(atom::Atom)

Returns the atomic mass of an atom given the Atom structure.

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Base.position — Function

position(atom::Atom)

Returns the position of an atom given the Atom structure.

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Custom Atom fields

Custom atom fields can be created in Atom objects by defining the custom keyword. By default, custom == nothing. The custom fields can be added on construction, or with the add_custom_field function, which creates a new instance of an Atom with the added value in the custom field:

For example:

julia> using PDBTools

julia> atom = Atom(custom="TEST");

julia> atom.custom
"TEST"

julia> atom = Atom(;name = "CA", resname="ALA"); # no custom field

julia> atom.resname
"ALA"

julia> new_atom = add_custom_field(atom, Dict(:charge => 2.0));

julia> new_atom.resname
"ALA"

julia> new_atom.custom[:charge]
2.0

PDBTools.add_custom_field — Function

add_custom_field(atom::Atom, value)

Adds a custom field to an Atom structure, returning a new Atom structure with the custom field added. The returning Atom structure is parameterized with the type of value.

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Elements for custom atom types

The types of atoms that PDBTools recognizes is defined in the PDBTools.elements dictionary. If new atom types are defined, it is possible to add these types to the dictionary, such that other functions work for the new types. The function to be used is add_element!.

PDBTools.add_element! — Function

add_element!(symbol::String, reference_element::PDBTools.Element; elements=PDBTools.elements)

Add a new element to the elements dictionary. If the element already exists, overwrite it.

To remove all custom elements, use remove_custom_elements!().

Example

julia> using PDBTools

julia> remove_custom_elements!(); # if any

julia> atoms = [ Atom(name="A1"), Atom(name="A2") ];

julia> add_element!("A1", PDBTools.elements["C"])
PDBTools.Element(:C, "C", "Carbon", 6, 12.011, true)

julia> add_element!("A2", PDBTools.elements["N"])
PDBTools.Element(:N, "N", "Nitrogen", 7, 14.0067, true)

julia> element(atoms[1])
"C"

julia> element(atoms[2])
"N"

julia> mass(atoms)
26.017699999999998

julia> remove_custom_elements!();

Here we repeteadly call remove_custom_elements!() to guarantee the proper execution of the test codes, without any custom elements predefined.

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PDBTools.remove_custom_elements! — Function

remove_custom_elements!()

Remove all custom elements from the elements dictionary.

Example

julia> using PDBTools

julia> remove_custom_elements!();

julia> add_element!("GN", PDBTools.elements["N"])
PDBTools.Element(:N, "N", "Nitrogen", 7, 14.0067, true)

julia> element(Atom(name="GN"))
"N"

julia> remove_custom_elements!();

julia> element(Atom(name="GN")) # returns `nothing`

Here we repeteadly call remove_custom_elements!() to guarantee the proper execution of the test codes, without any custom elements predefined.

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