Abstract | BACKGROUND: . Mycobacterium tuberculosis is the single most deadly human pathogen and is responsible for nearly three million deaths every year. Recent elucidation of the mode of action of isoniazid, a frontline antimycobacterial drug, suggests that NAD metabolism is extremely critical for this microorganism. M. tuberculosis depends solely on the de novo pathway to meet its NAD demand. Quinolinic acid phosphoribosyltransferase ( QAPRTase), a key enzyme in the de novo biosynthesis of NAD, provides an attractive target for designing novel antitubercular drugs. RESULTS: . The X-ray crystal structure of the M. tuberculosis QAPRTase apoenzyme has been determined by multiple isomorphous replacement at 2.4 A resolution. Structures of the enzyme have also been solved in complex with the substrate quinolinic acid (QA), the inhibitory QA analog phthalic acid (PA), the product nicotinate mononucleotide (NAMN), and as a ternary complex with PA and a substrate analog, 5-phosphoribosyl-1-(beta-methylene)pyrophosphate (PRPCP). The structure of the nonproductive QAPRTase-PA-PRPCP Michaelis complex reveals a 5-phosphoribosyl-1-pyrophosphate-binding site that is different from the one observed in type I phosphoribosyltransferases (PRTases). The type II PRTase active site of QAPRTase undergoes conformational changes that appear to be important in determining substrate specificity and eliciting productive catalysis. CONCLUSIONS: . QAPRTase is the only known representative of the type II PRTase fold, an unusual alpha/beta barrel, and appears to represent convergent evolution for PRTase catalysis. The active site of type II PRTase bears little resemblance to the better known type I enzymes.
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Authors | V Sharma, C Grubmeyer, J C Sacchettini |
Journal | Structure (London, England : 1993)
(Structure)
Vol. 6
Issue 12
Pg. 1587-99
(Dec 15 1998)
ISSN: 0969-2126 [Print] United States |
PMID | 9862811
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
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Chemical References |
- Antitubercular Agents
- Recombinant Proteins
- Nicotinamide Mononucleotide
- nicotinate mononucleotide
- Pentosyltransferases
- nicotinate-nucleotide diphosphorylase (carboxylating)
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Topics |
- Amino Acid Sequence
- Antitubercular Agents
(chemical synthesis, pharmacology)
- Crystallography, X-Ray
- Drug Design
- Humans
- Molecular Sequence Data
- Mycobacterium tuberculosis
(drug effects, enzymology)
- Nicotinamide Mononucleotide
(analogs & derivatives, metabolism)
- Pentosyltransferases
(chemistry, metabolism)
- Protein Conformation
- Recombinant Proteins
(chemistry, isolation & purification, metabolism)
- Sequence Homology, Amino Acid
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