Se Woong Kim

Insights into noncanonical E1 enzyme activation from the structure of autophagic E1 Atg7 with Atg8

Autophagy is the degradation of cellular organelles via the lysosomal pathway. The autophagic ubiquitin-like (Ubl) molecule Atg8 is activated by the E1-like enzyme Atg7. As this noncanonical E1 enzymes domain organization is unique among Ubl-activating E1 enzymes, the structural basis for its interactions with Atg8 and partner E2 enzymes remains obscure. Here we present the structure of the N-terminal domain of Atg7, revealing a unique protein fold and interactions with both autophagic E2 enzymes Atg3 and Atg10. The structure of the C-terminal domain of Atg7 in complex with Atg8 shows the mode of dimerization and mechanism of recognition of Atg8. Notably, the catalytic cysteine residue in Atg7 is positioned close to the C-terminal glycine of Atg8, its target for thioester formation, potentially eliminating the need for large conformational rearrangements characteristic of other E1s.

Asc1p, a ribosomal protein, plays a pivotal role in cellular adhesion and virulence in Candida albicans

Candida albicans, the common human fungal pathogen, can switch morphology from yeast to pseudohyphal or hyphal form upon various environmental cues. It is well-known that the ability of morphological conversion and adhesive growth renders C. albicans virulent. It is noteworthy that every factor involved in the morphogenesis is known to be important for the virulence of this pathogen. To examine a functional relevance of Asc1p, a ribosomal protein, in morphogenesis and virulence, an asc1 homozygous null mutant was generated. Although a normal morphological transition of the asc1 deletion strain in liquid media was found, it did not change its morphology on solid media. Moreover, the adhesion activity and hyphal-specific gene expression were defective due to ASC1 deletion. Finally, it was found that the asc1 null mutant was avirulent in a mouse model. These results strongly suggested that Asc1p a component of the 40S ribosomal subunit and a signal transducer, plays a pivotal role in cellular adhesion and virulence through regulation of specific gene expression in C. albicans.