Structures of Pathogenic Fungal FKBP12s Reveal Possible Self-Catalysis Function

Area of Science:

• Biochemistry
• Structural Biology
• Mycology

Background:

• Invasive fungal infections are challenging to treat, necessitating novel therapeutic strategies.
• The 12-kDa FK506-binding protein (FKBP12) is a conserved peptidyl-prolyl isomerase in fungal pathogens, making it a potential panfungal drug target.
• The substrates and mechanisms of FKBP12s remain largely unknown, hindering drug development.

Purpose of the Study:

• To investigate the structural and biochemical properties of FKBP12 from pathogenic fungi, including Candida albicans, Candida glabrata, and Aspergillus fumigatus.
• To elucidate the potential self-substrate interaction and catalytic mechanism of fungal FKBP12.
• To provide a basis for developing novel antifungal therapies targeting FKBP12.

Main Methods:

• X-ray crystallography was used to determine the structures of apo FKBP12 from A. fumigatus and C. albicans.
• Biochemical assays, including cysteine cross-linking, were performed to investigate protein interactions.
• In vivo genetic studies were conducted to assess the functional impact of FKBP12 mutations.

Main Results:

• Crystal structures revealed a unique intermolecular interaction where an active-site proline inserts into an adjacent FKBP12 subunit's active site.
• This self-substrate interaction was observed in both cis and trans proline conformations, supporting self-catalysis.
• Cysteine cross-linking confirmed the formation of FKBP12 dimers in solution, and genetic studies indicated transient dimeric states in vivo.

Conclusions:

• Fungal FKBP12s exhibit a novel self-substrate regulatory mechanism involving intermolecular proline insertion.
• This unique mechanism provides new understanding of FKBP12 function in pathogenic fungi.
• The findings support FKBP12 as a promising target for developing broad-spectrum antifungal drugs.