A classical enzyme active center motif lacks catalytic competence until modulated electrostatically.

  title={A classical enzyme active center motif lacks catalytic competence until modulated electrostatically.},
  author={Surapong Pinitglang and Aaron Watts and M. Patel and James D. Reid and Michael A. Noble and Sheraz Gul and A Bokth and Ahmed Muhammad Naeem and H Patel and Emrys W. Thomas and Sreejesh Sreedharan and Chandra S Verma and Keith Brocklehurst},
  volume={36 33},
The cysteine proteinase superfamily is a source of natural structural variants of value in the investigation of mechanism. It has long been considered axiomatic that catalytic competence of these enzymes mirrors the generation of the ubiquitous catalytic site imidazolium-thiolate ion pair. We here report definitive evidence from kinetic studies supported by electrostatic potential calculations, however, that at least for some of these enzymes the ion pair state which provides the nucleophilic… 
Electrostatic properties in the catalytic site of papain: A possible regulatory mechanism for the reactivity of the ion pair
The electrostatic profile found in the proton transfer region of papain showed that this enzyme has a well‐defined electrostatic environment to favor the formation and stabilization of the catalytic ion pair, and describes a possible regulatory mechanism controlling the ion pair reactivity.
Generation of nucleophilic character in the Cys25/His159 ion pair of papain involves Trp177 but not Asp158.
Investigation of papain studies using a new series of cationic aminoalkyl 2-pyridyl disulfide time-dependent inhibitors as reactivity probes leads to the conclusion that Asp158 is not involved in the generation of nucleophilic character in the ion pair and demonstrates a key role for Trp177.
Identification of interactions involved in the generation of nucleophilic reactivity and of catalytic competence in the catalytic site Cys/His ion pair of papain.
A key result is the correlation between the kinetic influence of the modulatory trigger of pK(a) 4 and disruption of the hydrogen bond donated by the indole N-H of Trp177, the hydrophobic shield of the initial "intimate" ion pair.
Challenging a paradigm: Theoretical calculations of the protonation state of the Cys25‐His159 catalytic diad in free papain
Applying the QM/SCRF(VS) molecular modeling approach, it is concluded that the His–Cys catalytic diad in free papain is fully protonated, NH(+)/SH.
Structural Basis of Perturbed pKa Values of Catalytic Groups in Enzyme Active Sites
The p K a values of catalytic groups that are found in the active sites of numerous enzymes are significantly more perturbed (>2 units) and are the subject of this review.
The only active mutant of thymidylate synthase D169, a residue far from the site of methyl transfer, demonstrates the exquisite nature of enzyme specificity.
Cysteine is the only variant of D169, a cofactor-binding residue in thymidylate synthase, that shows in vivo activity and changes to partitioning among productive and non-productive conformations of reaction intermediates may contribute as much, if not more, to the diminished activity of this mutant.
Factors affecting protein thiol reactivity and specificity in peroxide reduction.
It is proposed that the set of interactions is better described as a means of stabilizing the anionic transition state of the reaction, and the enhanced acidity of the critical cysteine is concurrent but not the cause of catalytic efficiency.
Catalytic Site pKa Values of Aspartic, Cysteine, and Serine Proteases: Constant pH MD Simulations
This work uses single pH constant pH MD simulations as a fast and robust tool to estimate the active site pKa values of a set of aspartic, cysteine, and serine proteases, and captures characteristic pKa shifts of theactive site residues, which dictate the experimentally determined activity profiles of the respective protease family.
Biochemical and X‐ray crystallographic studies on shikimate kinase: The important structural role of the P‐loop lysine
From studies of ligand binding it appears that, like adenylate kinase, shikimate kinase binds substrates randomly and in a synergistic fashion, indicating that the two enzymes have similar catalytic mechanisms.
Sortase from Staphylococcus aureus Does Not Contain a Thiolate-Imidazolium Ion Pair in Its Active Site*
A peptidyl-vinyl sulfone substrate mimic is synthesized that irreversibly inhibits SrtA and measurements are inconsistent with the existence of a thiolate-imidazolium ion pair and suggest a general base catalysis mechanism during transpeptidation.