A structural determinant of mycophenolic acid resistance in eukaryotic inosine 5'-monophosphate dehydrogenases

Area of Science:

• Biochemistry
• Molecular Biology
• Mycology

Background:

• Mycophenolic acid (MPA) is a natural inhibitor of inosine 5'-monophosphate dehydrogenases (IMPDHs).
• Fungal IMPDHs from Penicillium brevicompactum are resistant to MPA, despite having identical binding sites to sensitive IMPDHs.
• The structural basis for MPA resistance in these fungal enzymes was previously unknown.

Purpose of the Study:

• To identify the structural determinants responsible for MPA resistance in fungal IMPDHs.
• To investigate the role of specific amino acid residues in MPA sensitivity and resistance.
• To explore the evolutionary implications of these findings in fungal IMPDHs.

Main Methods:

• Site-directed mutagenesis was used to substitute specific amino acid residues in fungal IMPDHs.
• Enzyme activity assays were performed to assess MPA sensitivity before and after mutations.
• Comparative analysis of amino acid sequences across different fungal species.

Main Results:

• A single residue, Serine 267 (Ser267), was identified as the key determinant of MPA resistance in Penicillium brevicompactum IMPDH (PbIMPDHA).
• Substituting Ser267 with Alanine (Ala) in PbIMPDHA rendered the enzyme sensitive to MPA.
• Conversely, substituting the analogous Alanine residue with Serine in Aspergillus nidulans IMPDH conferred MPA resistance, with minimal impact on catalytic efficiency.

Conclusions:

• The Ser267 residue is a critical factor conferring Mycophenolic acid resistance in fungal IMPDHs.
• This single amino acid substitution has significant implications for understanding drug resistance mechanisms.
• The prevalence of Ser/Threonine at position 267 in certain Aspergillus species may indicate an evolutionary adaptation to MPA exposure.