Enhanced activity of α-chymotrypsin in organic media using designed molecular staples

Easy and Selective Method for the Synthesis of Mono-, Di-, Tri-, Tetra-O-Arylmethyl-P-T-Butylcalix[4]Arenes

Mono-, di-, tri- and tetra-O-arylmethyl-p-t-butylcalix[4]arenes were synthesised respectively from p-t-butylcalix[4]arene and arylmethyl bromide through an easy and selective one-step reaction. Mono- and di-arylmethyl ethers of p-t-butylcalix[4]arenes were prepared using LiH as a base, while tri- and tetra-arylmethyl derivatives were afforded in the presence of Ba(OH)2 and BaO. These methods are remarkable for excellent selectivity, mild reaction conditions, moderate to good yields and easy purification.

Modulation of the catalytic behavior of alpha-chymotrypsin at monolayer-protected nanoparticle surfaces

Amino-acid-functionalized gold clusters modulate the catalytic behavior of alpha-chymotrypsin (ChT) toward cationic, neutral, and anionic substrates. Kinetic studies reveal that the substrate specificity (k(cat)/K(M)) of ChT-nanoparticle complexes increases by approximately 3-fold for the cationic substrate but decreases by 95% for the anionic substrate as compared with that of free ChT, providing enhanced substrate selectivity. Concurrently, the catalytic constants (k(cat)) of ChT show slight augmentation for the cationic substrate and significant attenuation for the anionic substrate in the presence of amino-acid-functionalized nanoparticles. The amino acid monolayer on the nanoparticle is proposed to control both the capture of substrate by the active site and release of product through electrostatic interactions, leading to the observed substrate specificities and catalytic constants.

Sugar-mediated lyoprotection of purified human CYP3A4 and CYP2D6

P450 enzymes are of great interest for drug metabolism and as potential biocatalysts. Like most P450s, purified CYP3A4 is normally handled and stored in solution because lyophilization greatly reduces its activity. We show here that colyophilization of this enzyme with sucrose or trehalose, but not mannitol, crown ethers or cyclodextrins, allow recovery of full enzymatic activity after rehydration. Sorbitol was almost as efficient, with 85% retention of the original activity. We also show that similar protection is observed through colyophilization of CYP2D6 with trehalose. This procedure should greatly facilitate handling, storage, or use of these enzymes in anhydrous media.

On the relationship between the activity and structure of PEG-alpha-chymotrypsin conjugates in organic solvents

Enzymes are attractive catalysts for the production of optically active compounds in organic solvents. However, their often low catalytic activity in such applications hampers their practical use. To overcome this, we investigated the effectiveness of the covalent modification of alpha-chymotrypsin with methoxy poly(ethylene glycol) (PEG) with a Mw of 5,000 to enhance its activity. The model transesterification reaction between sec-phenethyl alcohol and vinyl butyrate in various neat dry organic solvents and at a controlled water activity of 0.008 in two solvents was employed to measure the effect of PEGylation on activity and enantioselectivity. Synthesis conditions were varied to obtain various conjugates with average molar ratios of PEG-to-chymotrypsin ranging from ca. 1 to 7. While the enantioselectivity increased only modestly from ca. 4.4 to 6.1 when averaging results in all solvents, PEG was very efficient in increasing the activity of alpha-chymotrypsin up to more than 400-fold compared to that of the powder lyophilized from buffer alone. The activity increase was more pronounced in apolar than in polar organic solvents and also depended on the amount of PEG bound to the enzyme. For example, the activity of the modified enzyme towards the most reactive "S" enantiomer in octane increased 440-fold but increasing the molar ratio of PEG-to-enzyme from 1.1 to 7.1 resulted in a more than twofold decrease in enzyme activity. Controlling the water activity did not prevent the drop in activity. To investigate the possible origin of the activity changes, Fourier transform infrared (FTIR) spectroscopy experiments were conducted. It was found that PEGylation reduced lyophilization-induced structural perturbations, but exposure to the organic solvents caused structural perturbations. These perturbations were more pronounced in polar than in apolar solvents. The pronounced activity drop in polar solvents at increasing PEG-modification levels correlated with an increasing level of solvent-induced structural perturbations. This correlation was less pronounced in apolar solvents where both, activity drop and structural perturbations, were less pronounced at increasing PEGylation levels. In summary, PEG-modified alpha-chymotrypsin might be an interesting system to catalyze reactions, particularly in apolar organic solvents.