Ionization states of the catalytic residues in HIV-1 protease.
Chemical synthesis was used to prepare the HIV-1 protease specifically 13C-labelled in the catalytically essential Asp 25 in each monomer. The NMR chemical shift of the 13C-enriched homodimeric enzyme was measured in the presence of the inhibitor pepstatin, a mimic of the tetrahedral intermediate formed in enzyme catalysis. In this complex, the catalytic carboxyls do not titrate in the pH range where the enzyme is active; throughout the range pH 2.5-6.5, one Asp 25 side chain is protonated and the other deprotonated. By contrast, in the absence of inhibitor the two Asp side chains are chemically equivalent and both deprotonated at pH6, the optimum for enzymatic activity. These direct observations of the chemical properties of the catalytic apparatus of the enzyme provide concrete information on which to base the design of improved HIV-1 protease inhibitors.
Smith
R
R
Department of Biochemistry, University of Queensland, Australia. ross@biosci.uq.edu.au stevek@chemical.ligation.com
Brereton
I M
IM
Chai
R Y
RY
Kent
S B
SB
D001224:Aspartic Acid / Q000737:chemistry*; D002384:Catalysis; D016333:HIV Protease / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D017320:HIV Protease Inhibitors / Q000494:pharmacology; D015497:HIV-1 / Q000201:enzymology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions; D009682:Magnetic Resonance Spectroscopy; D010436:Pepstatins / Q000494:pharmacology
D017320:HIV Protease Inhibitors; D007477:Ions; D010436:Pepstatins; C014195:Streptomyces pepsin inhibitor; D001224:Aspartic Acid; D016333:HIV Protease; C031375:pepstatin