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Antimicrobial Agents and Chemotherapy, January 2009, p. 86-94, Vol. 53, No. 1
0066-4804/09/$08.00+0     doi:10.1128/AAC.00275-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Inhibition of Methionyl-tRNA Synthetase by REP8839 and Effects of Resistance Mutations on Enzyme Activity{triangledown}

Louis S. Green,{dagger} James M. Bullard,{dagger} Wendy Ribble, Frank Dean, David F. Ayers, Urs A. Ochsner, Nebojsa Janjic, and Thale C. Jarvis*

Replidyne, Inc., 1450 Infinite Dr., Louisville, Colorado 80027

Received 27 February 2008/ Returned for modification 9 June 2008/ Accepted 22 October 2008

REP8839 is a selective inhibitor of methionyl-tRNA synthetase (MetRS) with antibacterial activity against a variety of gram-positive organisms. We determined REP8839 potency against Staphylococcus aureus MetRS and assessed its selectivity for bacterial versus human orthologs of MetRS. The inhibition constant (Ki) of REP8839 was 10 pM for Staphylococcus aureus MetRS. Inhibition of MetRS by REP8839 was competitive with methionine and uncompetitive with ATP. Thus, high physiological ATP levels would actually facilitate optimal binding of the inhibitor. While many gram-positive bacteria, such as Staphylococcus aureus, express exclusively the MetRS1 subtype, many gram-negative bacteria express an alternative homolog called MetRS2. Some gram-positive bacteria, such as Streptococcus pneumoniae and Bacillus anthracis, express both MetRS1 and MetRS2. MetRS2 orthologs were considerably less susceptible to REP8839 inhibition. REP8839 inhibition of human mitochondrial MetRS was 1,000-fold weaker than inhibition of Staphylococcus aureus MetRS; inhibition of human cytoplasmic MetRS was not detectable, corresponding to >1,000,000-fold selectivity for the bacterial target relative to its cytoplasmic counterpart. Mutations in MetRS that confer reduced susceptibility to REP8839 were examined. The mutant MetRS enzymes generally exhibited substantially impaired catalytic activity, particularly in aminoacylation turnover rates. REP8839 Ki values ranged from 4- to 190,000-fold higher for the mutant enzymes than for wild-type MetRS. These observations provide a potential mechanistic explanation for the reduced growth fitness observed with MetRS mutant strains relative to that with wild-type Staphylococcus aureus.

* Corresponding author. Mailing address: Replidyne, Inc., 1450 Infinite Dr., Louisville, CO 80027. Phone: (303) 996-5500. Fax: (303) 996-5599. E-mail: thale.jarvis{at}gmail.com

{triangledown} Published ahead of print on 17 November 2008.

{dagger} These authors contributed equally to this work.

Antimicrobial Agents and Chemotherapy, January 2009, p. 86-94, Vol. 53, No. 1
0066-4804/09/$08.00+0     doi:10.1128/AAC.00275-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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