Role of N-terminal of metacaspase of Candida albicans in calcium binding.

Metacaspases are members of the CD clan and share structural similarities with mammalian caspases but possess unique features. This study delves into the Candida albicans metacaspase CaMCA-Ia, a type I metacaspase. CaMCA-Ia demonstrates Ca²⁺-dependent autoprocessing and presents a hydrophobic N-terminal, which differs from that of type II metacaspases. Truncated CaMCA-Ia (CaMCA-Ia-ΔN86), lacking 86 N-terminal amino acids, undergoes gradual self-processing and intermolecular processing. Calcium addition induces multistep processing, leading to maturation. Like mammalian caspases, CaMCA-Ia-ΔN86 can activate other molecules, indicate intermolecular activation and accelerating maturation. Distinct binding sites for the full-length and truncated forms of CaMCA-Ia in interaction with Ca²⁺ underscore the N-terminal's role in altering calcium affinity. These findings enhance the understanding of metacaspases' intricate activation and maturation dynamics, offering insights into potential drug targets for pathogenic fungi. The CaMCA mutants D252A, D268A, D299A, and D268/269 A display varied responses to calcium, while the corresponding CaMCA-Ia-ΔN86 mutants exhibit different processing patterns. The D268/299 A mutant showed processing after 48 h of incubation with calcium. Alterations in CaMCA structure and function, such as the deletion of the N-terminus and changes in the aspartates at the calcium-binding site, provide important insights into how CaMCA enzymatic activity and autoprocessing are regulated.