Search

Heparan sulfate (HS) and heparin contain imprinted "sulfation codes", which dictate their diverse physiological and pathological functions. A group of orchestrated biosynthetic enzymes cooperate in polymerizing and modifying HS chains. The biotechnological development of enzymes that can recreate this sulfation pattern on synthetic heparin is challenging, primarily due to the paucity of quantitative data for sulfotransferase enzymes. Herein, we identified critical structural characteristics that determine substrate specificity and shed light on the catalytic mechanism of sugar sulfation of two HS sulfotransferases, 2-O-sulfotransferase (HS2ST) and 6-O-sulfotransferase (HS6ST). Two sets of molecular clamps in HS2ST recognize appropriate substrates; these clamps flank the acceptor binding site on opposite sides. The hexuronic epimers, and not their puckers, have a critical influence on HS2ST selectivity. In contrast, HS6ST recognizes a broader range of substrates. This promiscuity is granted by a conserved tryptophan residue, W210, that positions the acceptor within the active site for catalysis by means of strong electrostatic interactions. Lysines K131 and K132 act in concert with a second tryptophan, W153, shedding water molecules from within the active site, thus providing HS6ST with a binding preference toward 2-O-sulfated substrates. QM/MM calculations provided valuable mechanistic insights into the catalytic process, identifying that the sulfation of both HS2ST and HS6ST follows a SN2-like mechanism. When they are taken together, our findings reveal the molecular basis of how these enzymes recognize different substrates and catalyze sugar sulfation, enabling the generation of enzymes that could create specific heparin epitopes., Competing Interests: The authors declare no competing financial interest.

The prototype Diels-Alder (DA) reaction between butadiene and ethene (system 1 ) and the DA reaction involving 1-methoxy-butadiene and cyano-ethylene (system 2 ) are investigated with an explicit-time-dependent Density Functional Theory approach. Bond orders and atomic net charges obtained in the dynamics at the transition state geometry and along the reaction coordinate toward reactants are used to provide a picture of the process in terms of VB/Lewis resonance structures that contribute to a resonance hybrid. The entire dynamics can be divided into different domains (reactant-like, product-like, and transition state domains) where different Lewis resonance structures contribute with different weights. The relative importance of these three domains varies along the reaction coordinate. In addition to the usual reactant-like and product-like covalent Lewis structures, ionic Lewis structures have non-negligible weights. In system 2 , the electron-donor OCH 3 on the diene and the electron-acceptor CN on the dienophile make more important the contributions of ionic Lewis structures that stabilize the transition state and determine the decrease of the reaction barrier with respect to system 1 .

The lack of solubility in water and the formation of aggregates hamper many opportunities for technological exploitation of C 60 . Here, different peptides were designed and synthesized with the aim of monomolecular dispersion of C 60 in water. Phenylalanines were used as recognizing moieties, able to interact with C 60 through π-π stacking, while a varying number of glycines were used as spacers, to connect the two terminal phenylalanines. The best performance in the dispersion of C 60 was obtained with the FGGGF peptidic nanotweezer at a pH of 12. A full characterization of this adduct was carried out. The peptides disperse C 60 in water with high efficiency, and the solutions are stable for months both in pure water and in physiological environments. NMR measurements demonstrated the ability of the peptides to interact with C 60 . AFM measurements showed that C 60 is monodispersed. Electrospray ionization mass spectrometry determined a stoichiometry of C 60 @(FGGGF) 4 . Molecular dynamics simulations showed that the peptides assemble around the C 60 cage, like a candy in its paper wrapper, creating a supramolecular host able to accept C 60 in the cavity. The peptide-wrapped C 60 is fully biocompatible and the C 60 "dark toxicity" is eliminated. C 60 @(FGGGF) 4 shows visible light-induced reactive oxygen species (ROS) generation at physiological saline concentrations and reduction of the HeLa cell viability in response to visible light irradiation.

In this paper we have examined the mechanism of tyrosine O-sulfonation catalyzed by human TPST-2. Our computations, in agreement with Teramoto's hypothesis, indicate a concerted SN2-like reaction (with an activation barrier of 18.2 kcal mol(-1)) where the tyrosine oxygen is deprotonated by Glu(99) (base catalyst) and simultaneously attacks as a nucleophile the sulfuryl group. For the first time, using a quantum mechanics protocol of alanine scanning, we identified unequivocally the role of the amino acids involved in the catalysis. Arg(78) acts as a shuttle that "assists" the sulfuryl group moving from the 3'-phosphoadenosine-5'-phosphosulfate molecule to threonine and stabilizes the transition state (TS) by electrostatic interactions. The residue Lys(158) keeps close the residues participating in the overall H-bond network, while Ser(285), Thr(81), and Thr(82) stabilize the TS via strong hydrogen interactions and contribute to lower the activation barrier.