Okamoto-Shibayama Kazuko, Kikuchi Yuichiro, Kokubu Eitoyo, Sato Yutaka, Ishihara Kazuyuki
Department of Microbiology, Tokyo Dental College, Chiyoda-ku, Tokyo, Japan.
FEMS Yeast Res. 2014 Jun;14(4):674-7. doi: 10.1111/1567-1364.12160. Epub 2014 May 23.
Csa2 is a member of both the Candida albicans Rbt5 protein family and the Common in Fungal Extracellular Membranes (CFEM) protein superfamily. CFEM proteins are characterized by an internal domain containing eight equally spaced cysteine residues. Csa2 is involved in iron uptake from hemoglobin and heme proteins; however, its precise role is unclear. Here, we provide quantitative evidence of the involvement of Csa2 in the utilization of iron from human hemoglobin during C. albicans hyphal growth. The ability of the hyphal form of the wild-type (wt), a homozygote csa2Δ mutant, and a complemented strain of C. albicans to utilize hemoglobin as an iron source under iron-restricted conditions was examined through growth studies and a crystal violet-staining assay. Hemoglobin-binding activity was assessed indirectly using a hemoglobin-sensitized tube method. Although hyphal growth of the wt and csa2Δ/Δ::CSA2 strains was completely recovered when a high concentration of human hemoglobin was added to the iron-restricted culture medium, the recovery of the csa2Δ/Δ mutant was significantly diminished. Furthermore, hemoglobin binding was impaired in the csa2Δ/Δ mutant compared with the wt and csa2Δ/Δ::CSA2 strains, revealing that Csa2 is involved in the utilization of hemoglobin as an iron source by the hyphal form of C. albicans.
Csa2是白色念珠菌Rbt5蛋白家族和真菌细胞外膜常见蛋白（CFEM）超家族的成员。CFEM蛋白的特征是其内部结构域含有八个等间距的半胱氨酸残基。Csa2参与从血红蛋白和血红素蛋白中摄取铁；然而，其确切作用尚不清楚。在此，我们提供了定量证据，证明Csa2在白色念珠菌菌丝生长过程中参与了从人血红蛋白中利用铁的过程。通过生长研究和结晶紫染色试验，检测了野生型（wt）、纯合子csa2Δ突变体以及白色念珠菌互补菌株的菌丝体在铁限制条件下将血红蛋白作为铁源利用的能力。使用血红蛋白敏化管法间接评估血红蛋白结合活性。虽然在铁限制培养基中添加高浓度人血红蛋白时，wt和csa2Δ/Δ::CSA2菌株的菌丝生长完全恢复，但csa2Δ/Δ突变体的恢复明显减弱。此外，与wt和csa2Δ/Δ::CSA2菌株相比，csa2Δ/Δ突变体中的血红蛋白结合受损，这表明Csa2参与了白色念珠菌菌丝体将血红蛋白作为铁源的利用过程。
