PAModel Objects

class PAModel(Model)

Class representation for a cobra model extended with enzyme kinetics as published in Alter et al. (2021).

Arguments:

id_or_model str or Model - String to use as model id, or actual model to base new model on. If a string, it is used as input to load a model from. If a model, a new model object is instantiated with the same properties as the original model (default None).
name str, optional - Human-readable string to be model description (default None).
p_tot float, optional - Total protein concentration (condition-dependent) (unit g_prot/g_cdw) (default 0.285).
senstitivity bool - Boolean value whether or not a sensitivity analysis should be performed during each simulation. This sensitivity analysis will indicate to which extent individual constraints contribute to the objective value. Enzyme sectors (EnzymeSector objects, optional): Information about the different enzyme sectors, including:
- Active_enzyme: Metabolic active proteins.
- Transl_enzyme: Enzymes related to translation.
- Unused_enzymes: Excess enzymes.
- Custom_enzymes (list): Custom enzyme sectors.
configuration Config object, optional - Information about the general configuration of the model, including identifier conventions. Default as defined in the PAModelpy.configuration script for the E.coli iML1515 model.

Attributes:

p_tot float - The fraction of biomass allocated to proteins (units: g_prot/g_cdw).
reactions DictList - A DictList where the key is the reaction identifier and the value is a Reaction.
metabolites DictList - A DictList where the key is the metabolite identifier and the value is a Metabolite.
genes DictList - A DictList where the key is the gene identifier and the value is a Gene.
name0 DictList - A DictList where the key is the group identifier and the value is a Group.
name1 DictList - A DictList where the key is the enzyme identifier and the value is an Enzyme.
name2 DictList - A DictList where the key is the enzyme variable identifier and the value is an EnzymeVariable.
name3 DictList - A DictList where the key is the catalytic event identifier and the value is a CatalyticEvent.
name4 dict - A dictionary containing sector-specific constraints.
name5 DictList - A DictList where the key is the sector identifier and the value is an EnzymeSector.

P_TOT_DEFAULT

g_protein/g_cdw

init

def __init__(id_or_model: Union[str, "Model", None] = None,
             name: Optional[str] = None,
             p_tot: Optional[float] = Config.P_TOT_DEFAULT,
             sensitivity: bool = True,
             active_sector: Optional[ActiveEnzymeSector] = None,
             translational_sector: Optional[TransEnzymeSector] = None,
             unused_sector: Optional[UnusedEnzymeSector] = None,
             custom_sectors: Union[List, CustomSector] = None,
             configuration=Config)

Constants

add_enzymes

def add_enzymes(enzyme_list: list) -> None

Add new enzymes to a model. Adapted from Cobra.core.model.add_reactions and Cobra.core.model.add_metabolites.

This function will add a DictList of enzymes to the model object and add new variables accordingly. For each enzyme-associated reaction, a constraint in each direction is added to the model. The change is reverted upon exit when using the model as a context.

Arguments:

enzyme_list list or Enzyme - A list of Enzyme objects. If it isn’t an iterable container, the enzyme will be placed into a list.

add_sectors

def add_sectors(sectors: List = None)

Adds sector variables to the model and adds these to the total protein constraint.

Arguments:

sectors list - A list of PAModelpy.EnzymeSectors to add to the model.

add_sector

def add_sector(sector)

Adds the sector variable for a specific sector to the model and adds this to the total protein constraint. Also stores the sector variables in the model attributes.

Arguments:

sector PAModelpy.EnzymeSector - The specific EnzymeSector to add to the model.

add_catalytic_events

def add_catalytic_events(catalytic_events: Optional[Iterable])

Add a new CatalyticEvent to the model. Will add a list of CatalyticEvent variables to the model object using the function defined in the CatalyticEvent object.

Arguments:

catalytic_events list or variables.CatalyticEvent - A list of variables.CatalyticEvent objects. If it isn’t an iterable container, the catalytic event will be placed into a list.

add_enzyme_constraints

def add_enzyme_constraints(constraint_list: Optional[list])

Add new enzyme constraints to a model. Will add a list of constraints to the model object and add new constraints accordingly. The change is reverted upon exit when using the model as a context.

Arguments:

constraint_list list, str, or constraints.Constraint - A list of constraints.Constraint objects. If it isn’t an iterable container, the constraint will be placed into a list. Also, a string with the constraint id can be provided. A constraint will be created before adding it to the model.

add_sector_constraints

def add_sector_constraints(constraint_list: Optional[list])

Add a new constraint related to a sector to a model. Will add a list of constraints to the model object and add new constraints accordingly. The change is reverted upon exit when using the model as a context.

Arguments:

constraint_list list or constraints.Constraint - A list of constraints.Constraint objects. If it isn’t an iterable container, the constraint will be placed into a list.

add_total_protein_constraint

def add_total_protein_constraint(p_tot: Optional[float] = P_TOT_DEFAULT)

Function which adds the total protein constraint to the model. This limits the amount of available enzymes and thus the resulting fluxes.

Notes:

The constraint expression looks like this:

``Etot - sum(E) + E_translprot + E_unusedprot == p_tot - E_trsn_0 - E_ue_0

Arguments:

p_tot float, optional - Fraction of biomass which consists of protein (g_protein/g_cdw). Default is 0.258 (E.coli).

add_reactions

def add_reactions(reaction_list: Iterable[Reaction]) -> None

Add reactions to the model. This method is superimposed upon the cobra.Model.add_reactions() function. As a new feature, it will add constraints to determine the lower and upper bound if a sensitivity analysis should be performed (which is determined by the model attribute: PAModel.sensitivity). Reactions with identifiers identical to a reaction already in the model are ignored. The change is reverted upon exit when using the model as a context.

Arguments:

reaction_list list - A list of cobra.Reaction objects.

add_lb_ub_constraints

def add_lb_ub_constraints()

Makes additional constraints for the reaction lower bounds and upperbounds. By adding these constraints the shadow prices of the reaction bounds can be calculated and used in sensitivity analysis

make_lb_ub_constraint

@staticmethod
def make_lb_ub_constraint(m: Optional[Model], rxn: Reaction,
                          lower_bound: float, upper_bound: float)

Adding variables and constraints for the lower and upper bounds of a reaction to a model. When solving the model, shadow prices for the lower and upper bounds will be calculated. This allows for the calculation of sensitivity coefficients. The constraints are formulated as follows:

Notes:

Constraints are formulated as follows:

R_ub: R_fwd - R_rev <= UB
R_lb: -(R_fwd - R_rev) <= -LB

Arguments:

m cobra.Model or PAModelpy.PAModel - The model to which the upper and lower bound constraints and variables should be added.
rxn cobra.Reaction - The reaction for which upper and lower bound constraints should be generated.
lower_bound float - The value of the lower bound.
upper_bound float - The value of the upper bound.

Returns:

m cobra.Model or PAModelpy.PAModel - The model with additional constraints and variables for the reactions.

make_enzyme_min_max_constraint

@staticmethod
def make_enzyme_min_max_constraint(m: Optional[Model], enz: Enzyme,
                                   lower_bound: float, upper_bound: float)

Adding variables and constraints for the lower and upper bounds of an enzyme’s concentration to a model. When solving the model, shadow prices for the lower and upper bounds will be calculated. This allows for the calculation of sensitivity coefficients.

Notes:

The constraints are formulated as follows:

E_ub: E <= Emax
E_lb: -E <= -Emin

Arguments:

m cobra.Model or PAModelpy.PAModel - The model to which the upper and lower bound constraints and variables should be added.
rxn PAModelpy.Enzyme - The enzyme for which minimal and maximal concentration constraints should be generated.
lower_bound float - The value of the lower bound.
upper_bound float - The value of the upper bound.

Returns:

m cobra.Model or PAModelpy.PAModel - The model with additional constraints and variables for the enzyme’s concentration.

parse_shadow_prices

@staticmethod
def parse_shadow_prices(shadow_prices)

Parse the shadow prices to a DataFrame where each constraint corresponds to a row, and shadow prices and directions are columns.

calculate_csc

def calculate_csc(obj_value, mu, mu_ub, mu_lb, mu_ec_f, mu_ec_b)

Calculate the capacity sensitivity coefficient for all inequality constraints in the model. The sum of all capacity sensitivity coefficients should equal 1 for growth maximization.

Capacity Sensitivity Coefficient Calculation: Capacity Sensitivity Coefficient = constraint_UB * shadowprice / obj_value

Arguments:

obj_value float - The objective value of the model.
mu DataFrame - Shadow prices for all constraints.
mu_ub DataFrame - Shadow prices for the reaction upper bound (UB) constraints.
mu_lb DataFrame - Shadow prices for the reaction lower bound (LB) constraints.
mu_ec_f DataFrame - Shadow prices for the constraints related to enzymatic catalysis of the forward reaction.
mu_ec_b DataFrame - Shadow prices for the constraints related to enzymatic catalysis of the backward reaction.

Returns:

None

Results are saved in the self.capacity_sensitivity_coefficients attribute as a DataFrame.

calculate_esc

def calculate_esc(obj_value, mu_ec_f, mu_ec_b)

Calculate enzyme sensitivity coefficients for the enzyme variables using their primal values, the objective value, and shadow prices according to the following relations:

Enzyme Sensitivity Coefficient Calculation: esc = enzyme_variable.primal * constraint.shadowprice / obj_value

Arguments:

obj_value float - The objective value from the most recent optimal solution.
mu_ec_f pd.DataFrame - Shadow prices for maximizing enzyme concentrations (forward variables).
mu_ec_b pd.DataFrame - Shadow prices for minimizing enzyme concentrations (reverse variables).

Returns:

None

Fills the PAModel.enzyme_sensitivity_coefficients dataframe with the calculated enzyme sensitivity coefficients.

calculate_sum_of_enzymes

def calculate_sum_of_enzymes()

Calculate the sum of all enzyme variables for a feasible solution.

Returns:

float - The sum of all enzyme variables in milligrams per gram of cell dry weight per hour (mg/gCDW/h).

change_total_protein_constraint

def change_total_protein_constraint(p_tot)

Change the fraction of biomass that is allocated to active proteins.

Arguments:

p_tot float - The new proteome fraction in grams of protein per gram of cell dry weight (g_protein/g_cdw).

change_reaction_bounds

def change_reaction_bounds(rxn_id: str,
                           lower_bound: float = None,
                           upper_bound: float = None)

Change the reaction bounds. If a sensitivity analysis is required, the bounds of the upper and lower bound constraints are adjusted.

Arguments:

rxn_id str - The string representing the reaction identifier to change.
lower_bound float, optional - The new value for the lower bound of the reaction (default is None).
upper_bound float, optional - The new value for the upper bound of the reaction (default is None).

change_enzyme_bounds

def change_enzyme_bounds(enzyme_id: str,
                         lower_bound: float = None,
                         upper_bound: float = None)

Change the enzyme bounds. If the model should be primed for performing a sensitivity analysis, the upper bound of the minimum and maximum enzyme concentration constraints are adjusted.

Arguments:

enzyme_id str - The string representing the enzyme identifier to change.
lower_bound float, optional - The new value for the minimal enzyme concentration (default is None).
upper_bound float, optional - The new value for the maximal enzyme concentration (default is None).

get_enzymes_with_reaction_id

def get_enzymes_with_reaction_id(rxn_id: str)

Return Enzyme objects associated with the reaction identifier through CatalyticEvent objects.

Arguments:

rxn_id str - The reaction identifier.

Returns:

DictList - A DictList of Enzyme objects associated with the reaction.

get_reactions_with_enzyme_id

def get_reactions_with_enzyme_id(enz_id: str)

Return a list of reaction identifiers associated with the enzyme identifier (EC number) through CatalyticEvent objects.

Arguments:

enz_id str - The enzyme identifier (EC number).

Returns:

List[str] - A list of reaction identifiers associated with the enzyme.

change_kcat_value

def change_kcat_value(enzyme_id: str, kcats: dict)

Change the turnover number (kcat) of the enzyme for a specific reaction.

Arguments:

enzyme_id str - The enzyme identifier.
kcats dict - A dictionary with reaction identifiers as keys and kcat values as values. Each kcat value should be a nested dictionary with f (forward) and b (backward) as keys, and the corresponding kcat values as values.

Example:

Example dictionary for the kcat parameter {'R1': {'f': 10.0, 'b': 5.0}, 'R2': {'f': 7.0, 'b': 3.0}}

remove_enzymes

def remove_enzymes(
        enzymes: Union[str, Enzyme, List[Union[str, Enzyme]]]) -> None

Remove enzymes from the model.

Arguments:

enzymes list, reaction, or str - A list with enzymes (Enzyme), or their IDs, to remove. Enzymes will be placed in a list. Strings will be placed in a list and used to find the enzymes in the model.

Notes:

The change is reverted upon exit when using the model as a context.

remove_reactions

def remove_reactions(reactions: Union[str, Reaction, List[Union[str,
                                                                Reaction]]],
                     remove_orphans: bool = False) -> None

Remove reactions from the model. Inherited from the cobrapy.core.remove_reactions() function.

Arguments:

reactions list, reaction, or str - A list with reactions (cobra.Reaction), or their IDs, to remove. Reactions will be placed in a list. Strings will be placed in a list and used to find the reactions in the model.
remove_orphans bool, optional - Remove orphaned genes and metabolites from the model as well (default False).

Notes:

The change is reverted upon exit when using the model as a context. Also removes associated CatalyticEvents if they exist.

remove_catalytic_events

def remove_catalytic_events(catalytic_events: Union[
    str, CatalyticEvent, List[Union[str, CatalyticEvent]]],
                            remove_orphans: bool = False) -> None

Remove catalytic events from the model.

Arguments:

reactions list, reaction, or str - A list with reactions (cobra.Reaction), or their IDs, to remove. Reactions will be placed in a list. Strings will be placed in a list and used to find the reactions in the model.
remove_orphans bool, optional - Remove orphaned genes and metabolites from the model as well (default False).

Notes:

The change is reverted upon exit when using the model as a context.

remove_sectors

def remove_sectors(
    sectors: Union[
        str,
        Sector,
        ActiveEnzymeSector,
        List[Union[str, Sector, ActiveEnzymeSector]],
    ]
) -> None

Remove sections from the model.

Also removes associated CatalyticEvents if they exist.

Arguments:

sectors list, sector, or str - A list with sector (PAModelpy.Sector or PAModelpy.ActiveEnzymeSector), or their IDs, to remove. A single sector will be placed in a list. Strings will be placed in a list and used to find the sector in the model.

test

def test(glc_flux: Union[int, float] = 10)

Test the proteome allocation model.

Arguments:

glc_flux float, optional - The glucose flux which limits the growth rate (units: mmol_glc/g_cdw/h, default=10).

pfba

def pfba(fraction_of_optimum: float = 1.0,
         proteins: bool = False,
         reactions: bool = True,
         exclude: List["str"] = [],
         objective: Union[Dict, "Objective", None] = None)

Perform pFBA (parsimonious Enzyme Usage Flux Balance Analysis) with a custom objective including:

All reactions
All proteins
All proteins and all reactions.

pFBA [1] adds the minimization of all fluxes to the objective of the model. This approach is motivated by the idea that high fluxes have a higher enzyme turnover, and since producing enzymes is costly, the cell will try to minimize overall flux while still maximizing the original objective function, e.g., the growth rate.

Arguments:

fraction_of_optimum float, optional - The fraction of optimum which must be maintained. The original objective reaction is constrained to be greater than the maximal value times the fraction_of_optimum (default 1.0).
objective dict or cobra.Model.objective, optional - A desired objective to use during optimization in addition to the pFBA objective. Dictionaries (reaction as the key, coefficient as the value) can be used for linear objectives (default None).
proteins bool, optional - Determines whether to include enzyme variables in the pFBA objective.
reactions bool, optional - Determines whether to include reaction variables in the pFBA objective.
exclude list of reaction ids, optional - Reactions to exclude from the minimization objective.

References:

[1] Lewis, N. E., Hixson, K. K., Conrad, T. M., Lerman, J. A., Charusanti, P., Polpitiya, A. D., Palsson, B. O. (2010). Omic data from evolved E. coli are consistent with computed optimal growth from genome-scale models. Molecular Systems Biology, 6, 390. doi:10.1038/msb.2010.47

reset_objective

def reset_objective()

Reseting the objective to the standard biomass maximization objective after pFBA

optimize

def optimize(objective_sense: Optional[str] = None,
             raise_error: bool = False) -> "Solution"

Optimize the model using flux balance analysis. Inherits from the cobra.Model.optimize() function and performs a sensitivity analysis after optimization if this is desired (by setting the PAModel.sensitivity attribute to True).

Arguments:

objective_sense {None, 'maximize', 'minimize'}, optional - Whether fluxes should be maximized or minimized. In case of None, the previous direction is used (default None).
raise_error bool - If true, raise an OptimizationError if solver status is not optimal (default False).

Returns:

Solution

Notes:

Only the most commonly used parameters are presented here. Additional parameters for cobra.solver may be available and specified with the appropriate keyword argument.

copy

def copy() -> "PAModel"

Provide a partial ‘deepcopy’ of the Model.

Adjusted from cobra.Model.copy().

All the Metabolite, Gene, Reaction, Enzyme, EnzymeVariable, Sector, and CatalyticEvent objects are created anew but in a faster fashion than deepcopy.

Returns:

PAModelpy.PAModel - A new model copy.

PAModel Objects

P_TOT_DEFAULT

__init__

add_enzymes

add_sectors

add_sector

add_catalytic_events

add_enzyme_constraints

add_sector_constraints

add_total_protein_constraint

add_reactions

add_lb_ub_constraints

make_lb_ub_constraint

make_enzyme_min_max_constraint

parse_shadow_prices

calculate_csc

calculate_esc

calculate_sum_of_enzymes

change_total_protein_constraint

change_reaction_bounds

change_enzyme_bounds

get_enzymes_with_reaction_id

get_reactions_with_enzyme_id

change_kcat_value

remove_enzymes

remove_reactions

remove_catalytic_events

remove_sectors

test

pfba

reset_objective

optimize

copy

init