The Candida albicans pH-regulated KER1 gene encodes a lysine/glutamic-acid-rich plasma-membrane protein that is involved in cell aggregation.
Immunoscreening of a Candida albicans cDNA library with a polyclonal germ-tube-specific antibody (pAb anti-gt) resulted in the isolation of a gene encoding a lysine/glutamic-acid-rich protein, which was consequently designated KER1. The nucleotide and deduced amino acid sequences of this gene displayed no significant homology with any other known sequence. KER1 encodes a 134 kDa lysine (14.5%)/glutamic acid (16.7%) protein (Ker1p) that contains two potential transmembrane segments. KER1 was expressed in a pH-conditional manner, with maximal expression at alkaline pH and lower expression at pH 4.0, and was regulated by RIM101. A Deltaker1/Deltaker1 null mutant grew normally but was hyperflocculant under germ-tube-inducing conditions, yet this behaviour was also observed in stationary-phase cells grown under other incubation conditions. Western blotting analysis of different subcellular fractions, using as a probe a monospecific polyclonal antibody raised against a highly antigenic domain of Ker1p (pAb anti-Ker1p), revealed the presence of a 134 kDa band in the purified plasma-membrane fraction from the wild-type strain that was absent in the homologous preparation from Deltaker1/Deltaker1 mutant. The pattern of cell-wall protein and mannoprotein species released by digestion with beta-glucanases, reactive towards pAbs anti-gt and anti-Ker1p, as well as against concanavalin A, was also different in the Deltaker1/Deltaker1 mutant. Mutant strains also displayed an increased cell-surface hydrophobicity and sensitivity to Congo red and Calcofluor white. Overall, these findings indicate that the mutant strain was affected in cell-wall composition and/or structure. The fact that the ker1 mutant had attenuated virulence in systemic mouse infections suggests that this surface protein is also important in host-fungus interactions.
Departamento de Microbiologia y Ecologia, Facultad de Farmacia, Universitat de València, Spain.
Amparo
A
Galán
Departamento de Microbiologia y Ecologia, Facultad de Farmacia, Universitat de València, Spain.
Manuel
M
Casanova
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universitat de València, Spain.
Amelia
A
Murgui
Department of Molecular and Cell Biology, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK.
Donna M
DM
MacCallum
Department of Molecular and Cell Biology, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK.
Frank C
FC
Odds
Department of Molecular and Cell Biology, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK.
Neil A R
NAR
Gow
Departamento de Microbiologia y Ecologia, Facultad de Farmacia, Universitat de València, Spain.
José P
JP
Martínez
D000818:Animals; D001483:Base Sequence; D002176:Candida albicans / Q000235:genetics* / Q000378:metabolism* / Q000472:pathogenicity; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D018698:Glutamic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D008811:Mice, Inbred DBA; D008969:Molecular Sequence Data; D010641:Phenotype; D013347:Subcellular Fractions / Q000378:metabolism; D014774:Virulence / Q000235:genetics
D004271:DNA, Fungal; D005656:Fungal Proteins; D008565:Membrane Proteins; D018698:Glutamic Acid; D008239:Lysine