Mercaptide-imidazolium ion-pair: The reactive nucleophile in papain catalysis

Mercaptide-imidazolium ion-pair: the reactive nucleophile in papain catalysis.

The hydrolysis of amino acid derivatives catalyzed by papain (EC 3.4.4.10) proceeds through the formation of an acyl-thiolenzyme intermediate (cf. refs. [ 1,2] ). The pH-rate profde of the formation of this intermediate displays a bell-shaped curve depending on the ionization of two groups with pK, values of about 4 and 8 [ 1,2]. In the light of the steric structure of the active site of papain...

Sortase from Staphylococcus aureus does not contain a thiolate-imidazolium ion pair in its active site.

Many surface proteins are anchored to the cell wall by the action of sortase enzymes, a recently discovered family of cysteine transpeptidases. As the surface proteins of human pathogens are frequently required for virulence, the sortase-mediated anchoring reaction represents a potential target for new anti-infective agents. It has been suggested that the sortase from Staphylococcus aureus (Srt...

Anchoring of Surface Proteins to the Cell Wall of Staphylococcus aureus II. CYSTEINE 184 AND HISTIDINE 120 OF SORTASE FORM A THIOLATE- IMIDAZOLIUM ION PAIR FOR CATALYSIS*

Anchoring of surface proteins to the cell wall of Staphylococcus aureus. Cysteine 184 and histidine 120 of sortase form a thiolate-imidazolium ion pair for catalysis.

Surface proteins of Staphylococcus aureus are anchored to the cell wall peptidoglycan by a mechanism requiring a C-terminal sorting signal with a LPXTG motif. Sortase cleaves polypeptides between the threonine and the glycine of the LPXTG motif. The carboxyl group of threonine is subsequently amide-linked to the amino group of peptidoglycan cross-bridges. The three-dimensional structure of sort...

Electrostatic properties in the catalytic site of papain: A possible regulatory mechanism for the reactivity of the ion pair.

We present an analysis of the electrostatic properties in the catalytic site of papain (EC 3.4.22.2), an archetype enzyme of the C1 cysteine proteinase family, and we investigate their possible role in the formation, stabilization and regulation of the Cys25((-))...His159((+)) catalytic ion pair. The electrostatic properties were computed using a reassociation method based in multicentered mult...