Differential secretion of Sap4-6 proteins in Candida albicans during hyphae formation

Section of Infectious Diseases, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan 1 Department of Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan 2 Institute of Molecular Medicine, College of Medicine, National Taiwan University, 7 Chung Shan South Road, Taipei, Taiwan 3 Author for correspondence: Fang-Jen S. Lee. Tel: +886 2 2312 3456 ext. 5730. Fax: +886 2 2395 7801. e-mail: fangjen{at}ha.mc.ntu.edu.tw Secreted aspartyl proteinases (Saps) from Candida albicans are encoded by a multi-gene family and are considered to be putative virulence factors for candidiasis. SAP4–6 mRNAs were first detected during hyphae formation and were assumed to play roles in the development of disseminated candidiasis. Recombinant Sap proteins (Sap2–6) were prepared and specific antibodies were generated against Sap2–6. The presence of Sap4, Sap5 and Sap6, but not Sap2 or Sap3, was demonstrated in culture supernatants of C. albicans after induction of hyphae formation. In parallel to hyphae formation, Sap5 ( 40 kDa) was detected as early as 6 h after induction at neutral pH, and Sap4/6 ( 43 kDa) were detected after 24 h when the culture medium became acidic. The differential secretion of Sap5 and Sap4/6 was affected when the culture medium pH was buffered at pH 6·5 or pH 4·5. In addition, intracellular pools of Sap4–6 seem to exist, and protein is not necessary for Sap4–6 induction. This study provides the first evidence that Sap4–6 proteins in C. albicans are differentially produced and secreted during hyphae formation. Keywords: Candida albicans , secreted aspartyl proteinase, virulence factor, candidiasis Abbreviations: Sap, secreted aspartyl proteinase