protein.info: Summaries of thermodynamic properties of proteins

Description

Protein information, length, chemical formula, thermodynamic properties by group additivity, reaction coefficients of basis species, and metastable equilibrium example calculation.

Usage

pinfo(protein, organism=NULL, residue=FALSE)
  protein.length(protein, organism = NULL)
  protein.formula(protein, organism = NULL, residue = FALSE)
  protein.OBIGT(protein, organism = NULL, state=thermo()$opt$state)
  protein.basis(protein, T = 25, normalize = FALSE)

Arguments

protein: character, names of proteins; numeric, species index of proteins; data frame; amino acid composition of proteins
organism: character, names of organisms
residue: logical, return per-residue values (those of the proteins divided by their lengths)?
normalize: logical, return per-residue values (those of the proteins divided by their lengths)?
state: character, physical state
T: numeric, temperature in °C

Details

For character protein, pinfo returns the rownumber(s) of thermo()$protein that match the protein names. The names can be supplied in the single protein argument (with an underscore, denoting protein_organism) or as pairs of proteins and organisms. NA is returned for any unmatched proteins, including those for which no organism is given or that do not have an underscore in protein.

For numeric protein, pinfo returns the corresponding row(s) of thermo()$protein. Set residue to TRUE to return the per-residue composition (i.e. amino acid composition of the protein divided by total number of residues).

For dataframe protein, pinfo returns it unchanged, except for possibly the per-residue calculation.

The following functions accept any specification of protein(s) described above for pinfo:

protein.length returns the lengths (number of amino acids) of the proteins.

protein.formula returns a stoichiometrix matrix representing the chemical formulas of the proteins that can be pased to e.g. mass or ZC. The amino acid compositions are multiplied by the output of group.formulas to generate the result.

protein.OBIGT calculates the thermodynamic properties and equations-of-state parameters for the completely nonionized proteins using group additivity with parameters taken from Dick et al., 2006 (aqueous proteins) and LaRowe and Dick, 2012 (crystalline proteins and revised aqueous methionine sidechain group). The return value is a data frame in the same format as thermo()$OBIGT. state indicates the physical state for the parameters used in the calculation (aq or cr).

The following functions also depend on an existing definition of the basis species:

protein.basis calculates the numbers of the basis species (i.e. opposite of the coefficients in the formation reactions) that can be combined to form the composition of each of the proteins. The basis species must be present in thermo()$basis, and if H+ is among the basis species, the ionization states of the proteins are included. The ionization state of the protein is calculated using ionize.aa at the pH defined in thermo()$basis and at the temperature specified by the T argument. If normalize is TRUE, the coefficients on the basis species are divided by the lengths of the proteins.

References

Dick JM, LaRowe DE, Helgeson HC. 2006. Temperature, pressure, and electrochemical constraints on protein speciation: Group additivity calculation of the standard molal thermodynamic properties of ionized unfolded proteins. Biogeosciences 3: 311--336. tools:::Rd_expr_doi("10.5194/bg-3-311-2006")

LaRowe DE, Dick JM. 2012. Calculation of the standard molal thermodynamic properties of crystalline peptides. Geochim Cosmochim Acta 80: 70--91. tools:::Rd_expr_doi("10.1016/j.gca.2011.11.041")

Examples

Run this code

reset()
# Search by name in thermo()$protein
# These are the same: ip1 == ip2
ip1 <- pinfo("LYSC_CHICK")
ip2 <- pinfo("LYSC", "CHICK")
# Two organisms with the same protein name
ip3 <- pinfo("MYG", c("HORSE", "PHYCA"))
# Their amino acid compositions
pinfo(ip3)
# Their thermodynamic properties by group additivity
protein.OBIGT(ip3)

# An unknown protein name gives NA
ip4 <- pinfo("MYGPHYCA")

## Example for chicken lysozyme C
# Index in thermo()$protein
ip <- pinfo("LYSC_CHICK")
# Amino acid composition
pinfo(ip)
# Protein length and chemical formula
protein.length(ip)
protein.formula(ip)
# Group additivity for thermodynamic properties and HKF equation-of-state
# parameters of non-ionized protein
protein.OBIGT(ip)
# Calculation of standard thermodynamic properties
# (subcrt uses the species name, not ip)
subcrt("LYSC_CHICK")
# NOTE: subcrt() only shows the properties of the non-ionized
# protein, but affinity() uses the properties of the ionized
# protein if the basis species have H+

## These are all the same
protein.formula("P53_PIG")
protein.formula(pinfo("P53_PIG"))
protein.formula(pinfo(pinfo("P53_PIG")))