Active site properties of the 3C proteinase from hepatitis A virus (a hybrid cysteine/serine protease) probed by Raman spectroscopy

Effect of Plant-Derived Proteases on Infectivity of Tulane Virus, Murine Norovirus, and Hepatitis A Virus

ABSTRACT

Plant-derived proteases, bromelain, papain, and ficin, are broad-acting enzymes with generally recognized as safe status for foods and have current application in several food industries. These proteases have also been reported to have antimicrobial properties. This study investigated the efficacy of commercially prepared bromelain, papain, and ficin, individually and combined (2,500 ppm of crude extract), for inactivation of hepatitis A virus (HAV) and human norovirus surrogates, Tulane virus (TV), and murine norovirus (MNV). Various treatment temperatures (45, 50, or 55°C), times (10 or 60 min), and pH values (5.5 or 7.0) in the presence of cysteine (2 mM) were evaluated. Inactivation was assessed by infectivity in plaque assay for TV and MNV and by median tissue culture infective dose for HAV. No reduction in infectious TV or HAV was attributed to the plant-derived proteases at any of the conditions tested. Infectious MNV was reduced by 1 to 3 log PFU/mL; the most effective treatment was bromelain at pH 7 and 50°C for 10 min. A time course study with MNV in bromelain at 50°C indicated that a 2-log PFU/mL reduction could be achieved within 6 min, but extended treatment of 15 min was still insufficient to eliminate infectious MNV. The lack of or limited efficacy of bromelain, papain, and ficin on HAV, TV, and MNV, even at elevated temperatures and exposure times, suggests the plant-derived proteases are not commercially applicable for inactivation of virus on commodities or materials that could not also withstand mild heat treatment. The variable susceptibilities observed between TV and MNV illustrate limitations in utilization of surrogates for predicting pathogen behavior for a structure-specific treatment.

HIGHLIGHTS

Dispersive and FT-Raman spectroscopic methods in food analysis

Raman spectroscopy is a powerful technique for molecular analysis of food samples.

Synthesis of pdCpAs and transfer RNAs activated with thiothreonine and derivatives

N,S-diprotected L-thiothreonine and L-allo-thiothreonine derivatives were synthesized using a novel chemical strategy, and used for esterification of the dinucleotide pdCpA. The aminoacylated dinucleotides were then employed for the preparation of activated suppressor tRNA(CUA) transcripts. Thiothreonine and allo-thiothreonine were incorporated into a predetermined position of a catalytically competent dihydrofolate reductase (DHFR) analogue lacking cysteine, and the elaborated proteins were derivatized site-specifically at the thiothreonine residue with a fluorophore.

Synthesis of pdCpAs and transfer RNAs activated with derivatives of aspartic acid and cysteine

Described herein is the preparation of new aminoacylated derivatives of the dinucleotide pdCpA, and of transfer RNAs. The focus of the present work is the synthesis of amino acid analogs related to aspartic acid and cysteine species that have important functional roles in many proteins. The activated aminoacyl-tRNAs prepared can be utilized for the elaboration of proteins containing modified aspartic acid and cysteine derivatives at predetermined sites. Of particular interest is definition of functional group protection strategies that can be used for the preparation of the aminoacylated pdCpAs and tRNAs.

Molecular structure of 5-methyl thiophene acryloyl ethyl thiolester: a vibrational spectroscopic and density functional theory study

Enzyme-substrate intermediates involving the acyl group 5-methyl thiophene acryloyl (5-MTA) bound to the active site of an enzyme via a sulfur or selenium atom have been characterized by Raman spectroscopy (e.g., J. D. Doran and P. R. Carey, Biochemistry 1996, 35, 12495-12502, and M. J. O'Connor et al., J Amer Chem Soc 1996, 118, 239-240). Raman difference spectra reveal the Raman spectrum of the acyl group in the active site and, in turn, these can be used to probe acyl group conformation and active site forces and interactions. In order to improve the understanding of the relationship between conformational states and vibrational spectra of 5-MTA thiolesters, calculations based on a density functional theory analysis are undertaken for 5-methyl thiophene acryloyl ethyl ester. The calculations provide the precise geometries and energies of rotomers of 5-MTA ethyl thiolester involving rotational isomerism about the C--C single bonds flanking the ethylenic linkage and the S--C bond linking the ethyl group to the sulfur atom. The calculations also provide the vibrational spectrum for each conformer and these predictions are compared with the experimental Raman an IR data for the thiolester in carbon tetrachloride. Modes are identified that can act as conformational markers for isomerism about the C--C and S--C2H5 single bonds. These findings are used to identify the two conformational states giving rise to the Raman spectrum of the 5-MTA-S-enzyme formed by the viral cysteine protease HAV-3C.