PSMD Facilities: Biomedical EPR

Tyr and Trp spectra simulation algorithms (TRSSA)


What is TRSSA? By this acronym we refer to our two algorithms of simulation of the EPR spectra of two most frequently reported protein radicals – on tyrosines and tryptophans. The two TRSSA algorithms are different, clearly being functions of the radicals’ structures, but as both amino acid residues start from the same letter ‘t’, the acronym is the same for the two, and to distinguish one from the other, we use these formats: TRSSA-Y – Tyrosyl Radical Spectra Simulation Algorithm and TRSSA-W – Tryptophanyl Radical Spectra Simulation Algorithm. The advantage of using TRSSAs as compared to traditional Tyr and Trp radical EPR spectra simulation is in using as few as two input parameters that define (through the algorithms functions) all Hamiltonian parameters needed to perform an EPR spectra simulation.


A brief history of TRSSA algorithms

The first practical use of the methodology that has led to creation of the Tyrosyl Radical Spectra Simulation Algorithm (TRSSA) was reported in [1].

Shortly thereafter, the original algorithm for finding simulation parameters for Tyr radical was published [2]. In the supplemental material to the paper, which is a .zip file of several file folders, there is an Excel file called algorithm.xls.

The name TRSSA was used first a bit later, in [3].

A similar algorithm for tryptophanyl radicals was published in [4] and named TRSSA-W. From that point we started to refer to the original Tyr radical algorithm as TRSSA-Y, to distinguish one from the other.

TRSSA-Y has been updated with incorporation of Euler angles for the tensors of hyperfine interactions with methylene protons. The new version of TRSSA-Y detailed in the Supporting Information to the paper [5] can be downloaded as an Excel file by following this link.

TRSSA-W has been updated as reported at the 52nd Annual International Meeting of the ESR Spectroscopy Group of the Royal Society of Chemistry (University of Glasgow - 7-11 April 2019). The new version of the algorithm TRSSA-W v.2 can be downloaded from here.

Finally, the latest versions of TRSSA-Y and TRSSA-W have been developed as MatLab files for use with EasySpin, allowing simulations to be performed on this widely popular platform among EPR spectroscopists. These files are freely available; please contact us if you wish to use them.


[1] Svistunenko DA, Wilson MT, Cooper CE. Tryptophan or tyrosine? On the nature of the amino acid radical formed following hydrogen peroxide treatment of cytochrome c oxidase. Biochim Biophys Acta, 2004, 1655: 372-380.

[2] Svistunenko DA, Cooper CE. A new method of identifying the site of tyrosyl radicals in proteins. Biophys J, 2004, 87: 582-595.

[3] Svistunenko DA. Reaction of haem containing proteins and enzymes with hydroperoxides: The radical view. Biochim Biophys Acta, 2005, 1707: 127-155.

[4] Chaplin AK, Bernini C, Sinicropi A, et al. Tyrosine or Tryptophan? Modifying a metalloradical catalytic site by removal of the Cys-Tyr cross-link in the galactose 6-oxidase homologue GlxA. Angew Chem Int Ed Engl, 2017, 56: 6502-6506.

[5] Chaplin AK, Chicano TM, Hampshire BV, Wilson MT, Hough MA, Svistunenko DA and Worrall JAR. An aromatic dyad motif in dye decolourising peroxidases has implications for free radical formation and catalysis. Chemistry Eur J, 2019, in press, DOI: 10.1002/chem.201806290