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| IDENTIFICATION OF AMINO-ACID-RESIDUES INVOLVED IN THE BINDING OF HUPERZINE-A TO CHOLINESTERASES |
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| Author(s): SAXENA A, QIAN NF, KOVACH IM, KOZIKOWSKI AP, PANG YP, VELLOM DC, RADIC Z, QUINN D, TAYLOR P, DOCTOR BP |
| Source: PROTEIN SCIENCE Volume: 3 Issue: 10 Pages: 1770-1778 Published: OCT 1994 |
| Times Cited: 31 References: 25 |
| Abstract: Huperzine A, a potential agent for therapy in Alzheimer's disease and for prophylaxis of organophosphate toxicity, has recently been characterized as a reversible inhibitor of cholinesterases. To examine the specificity of this novel compound in more detail, we have examined the interaction of the 2 stereoisomers of Huperzine A with cholinesterases and site-specific mutants that detail the involvement of specific amino acid residues. Inhibition of fetal bovine serum acetylcholinesterase by (-)-Huperzine A was 35-fold more potent than (+)-Huperzine A, with K-I values of 6.2 nM and 210 nM, respectively. In addition, (-)-Huperzine A was 88-fold more potent in inhibiting Torpedo acetylcholinesterase than (+)-Huperzine A, with K-I values of 0.25 mu M and 22 mu M, respectively. Far larger K-I values that did not differ between the 2 stereoisomers were observed with horse and human serum butyrylcholinesterases. Mammalian acetylcholinesterase, Torpedo acetylcholinesterase, and mammalian butyrylcholinesterase can be distinguished by the amino acid Tyr, Phe, or Ala in the 330 position, respectively. Studies with mouse acetylcholinesterase mutants, Tyr 337(330) Phe and Tyr 337(330) Ala yielded a difference in reactivity that closely mimicked the native enzymes. In contrast, mutation of the conserved Glu 199 residue to Gin in Torpedo acetylcholinesterase produced only a 3-fold increase in K-I value for the binding of Huperzine A. Molecular mechanics energy minimization of the complexes formed between each of the 2 stereoisomers of Huperzine A and fetal bovine serum acetylcholinesterase, Torpedo acetylcholinesterase, or human butyrylcholinesterase also revealed that (-)-Huperzine A gave a better fit than (+)-Huperzine A and implicated Tyr 337(330) in the stereoselectivity of Huperzine A. |
| Document Type: Article |
| Language: English |
Addresses:
1. WALTER REED ARMY MED CTR, WALTER REED ARMY INST RES, DIV BIOCHEM, WASHINGTON, DC 20307 USA
2. CATHOLIC UNIV AMER, DEPT CHEM, WASHINGTON, DC 20064 USA
3. MAYO CLIN, JACKSONVILLE, FL 32224 USA
4. UNIV CALIF SAN DIEGO, LA JOLLA, CA 92093 USA
5. UNIV ZAGREB, INST MED RES, ZAGREB 41000, CROATIA
6. UNIV IOWA, DEPT CHEM, IOWA CITY, IA USA |
| Publisher: CAMBRIDGE UNIV PRESS, 40 WEST 20TH STREET, NEW YORK, NY 10011-4211 |
| Subject Category: Biochemistry & Molecular Biology |
| IDS Number: PR260 |
| ISSN: 0961-8368 |
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