microbiology, Vol 145, 1123-1135, Copyright © 1999 by Society for General Microbiology

ARTICLES

Purification of geranylgeranyltransferase I from Candida albicans and cloning of the CaRAM2 and CaCDC43 genes encoding its subunits

P Mazur, E Register, CA Bonfiglio, X Yuan, MB Kurtz, JM Williamson and R Kelly
Department of Biochemistry, Merck Research Laboratories, RY80Y-200, PO Box 2000, Rahway, NJ 07065, USA

All previously characterized protein geranylgeranyltransferases I (GGTase I) are heterodimeric zinc metalloenzymes which catalyse geranylgeranylation of a cysteine residue in proteins containing a C-terminal CaaL motif (C, Cys; a, aliphatic amino acid; L, Leu). The alpha and beta subunits of GGTase I of Saccharomyces cerevisiae are encoded by RAM2 and CDC43, respectively, and are essential for yeast viability. The authors are therefore investigating the role of geranylgeranylation in the related pathogenic yeast, Candida albicans, which is the most prevalent human fungal pathogen. GGTase I was purified to near homogeneity and also found to be a heterodimeric magnesium-dependent, zinc metalloenzyme displaying selectivity for CaaL-containing protein substrates. GGTase I peptide sequences were obtained from the purified protein and used to clone the genes encoding both subunits. CaRAM2 and CaCDC43 encode proteins that are 42 and 34% identical to their corresponding S. cerevisiae homologues, respectively, and 30% identical to their human homologues. Despite the limited overall homology, key zinc- and substrate-binding residues of the beta subunit (Cdc43p) are conserved. A unique feature of CaCdc43p is a tract of polyasparagine whose length varies from 6 to 17 residues among C. albicans strains and between alleles. Coexpression of both CaCDC43 and CaRAM2 under their native promoters complemented the ts defect of a S. cerevisiae cdc43 mutant but expression of the beta-subunit alone did not correct the growth defect, suggesting that hybrid GGTase I heterodimers are nonfunctional.

This article has been cited by other articles:

				J. L. Song and T. C. White RAM2: an essential gene in the prenylation pathway of Candida albicans Microbiology, January 1, 2003; 149(1): 249 - 259. [Abstract] [Full Text] [PDF]

				R. Kelly, D. Card, E. Register, P. Mazur, T. Kelly, K.-I. Tanaka, J. Onishi, J. M. Williamson, H. Fan, T. Satoh, et al. Geranylgeranyltransferase I of Candida albicans: Null Mutants or Enzyme Inhibitors Produce Unexpected Phenotypes J. Bacteriol., February 1, 2000; 182(3): 704 - 713. [Abstract] [Full Text]