TY - JOUR
T1 - The functional basis of mycophenolic acid resistance in Candida albicans IMP dehydrogenase
AU - Köhler, Gerwald A.
AU - Gong, Xin
AU - Bentink, Stefan
AU - Theiss, Stephanie
AU - Pagani, Gina M.
AU - Agabian, Nina
AU - Hedstrom, Lizbeth
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2005/3/25
Y1 - 2005/3/25
N2 - Candida albicans is an important fungal pathogen of immunocompromised patients. In cell culture, C. albicans is sensitive to mycophenolic acid (MPA) and mizoribine, both natural product inhibitors of IMP dehydrogenase (IMPDH). These drugs have opposing interactions with the enzyme. MPA prevents formation of the closed enzyme conformation by binding to the same site as a mobile flap. In contrast, mizoribine monophosphate, the active metabolite of mizoribine, induces the closed conformation. Here, we report the characterization of IMPDH from wild-type and MPA-resistant strains of C. albicans. The wild-type enzyme displays significant differences from human IMPDHs, suggesting that selective inhibitors that could be novel antifungal agents may be developed. IMPDH from the MPA-resistant strain contains a single substitution (A251T) that is far from the MPA-binding site. The A251T variant was 4-fold less sensitive to MPA as expected. This substitution did not affect the kcat value, but did decrease the Km values for both substrates, so the mutant enzyme is more catalytically efficient as measured by the value of kcat/ K m. These simple criteria suggest that the A251T variant would be the evolutionarily superior enzyme. However, the A251T substitution caused the enzyme to be 40-fold more sensitive to mizoribine monophosphate. This result suggests that A251T stabilizes the closed conformation, and this hypothesis is supported by further inhibitor analysis. Likewise, the MPA-resistant strain was more sensitive to mizoribine in cell culture. These observations illustrate the evolutionary challenge posed by the gauntlet of chemical warfare at the microbial level.
AB - Candida albicans is an important fungal pathogen of immunocompromised patients. In cell culture, C. albicans is sensitive to mycophenolic acid (MPA) and mizoribine, both natural product inhibitors of IMP dehydrogenase (IMPDH). These drugs have opposing interactions with the enzyme. MPA prevents formation of the closed enzyme conformation by binding to the same site as a mobile flap. In contrast, mizoribine monophosphate, the active metabolite of mizoribine, induces the closed conformation. Here, we report the characterization of IMPDH from wild-type and MPA-resistant strains of C. albicans. The wild-type enzyme displays significant differences from human IMPDHs, suggesting that selective inhibitors that could be novel antifungal agents may be developed. IMPDH from the MPA-resistant strain contains a single substitution (A251T) that is far from the MPA-binding site. The A251T variant was 4-fold less sensitive to MPA as expected. This substitution did not affect the kcat value, but did decrease the Km values for both substrates, so the mutant enzyme is more catalytically efficient as measured by the value of kcat/ K m. These simple criteria suggest that the A251T variant would be the evolutionarily superior enzyme. However, the A251T substitution caused the enzyme to be 40-fold more sensitive to mizoribine monophosphate. This result suggests that A251T stabilizes the closed conformation, and this hypothesis is supported by further inhibitor analysis. Likewise, the MPA-resistant strain was more sensitive to mizoribine in cell culture. These observations illustrate the evolutionary challenge posed by the gauntlet of chemical warfare at the microbial level.
UR - http://www.scopus.com/inward/record.url?scp=15744377146&partnerID=8YFLogxK
U2 - 10.1074/jbc.M409847200
DO - 10.1074/jbc.M409847200
M3 - Article
C2 - 15665003
AN - SCOPUS:15744377146
SN - 0021-9258
VL - 280
SP - 11295
EP - 11302
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 12
ER -