Heme-iron acquisition in fungi.

Heme is a bioavailable source of iron, for which different fungi have evolved several distinct acquisition mechanisms. In the iron-scarce animal host, in particular, microbial pathogens are able to utilize the large heme pool of hemoglobin. The opportunistic pathogenic fungus Candida albicans relies on a cascade of related extracellular soluble and cell wall-anchored hemophores to extract the heme from hemoglobin and to steer it across the cell wall to the plasma membrane, where it is endocytosed into the cell. Recent crystal structure determination of the soluble C. albicans hemophore Csa2 revealed a new protein fold with a unique heme-iron coordination, which suggests distinctive functional requirements for heme binding and transfer.