Domain organisation in phosphomannose isomerases (types I and II)

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Phosphomannose isomerase (PMI) is crucial for mannose metabolism.
• PMI exists in two main types, I and II, with distinct characteristics.
• Understanding PMI catalytic mechanisms is vital for various biological processes.

Purpose of the Study:

• To investigate the conserved protein motif in phosphomannose isomerase (PMI) types I and II.
• To determine if this motif is associated with the catalytic site and implies a common catalytic process.
• To elucidate the bifunctional nature of type II PMI, including its guanosine diphospho-D-mannose pyrophosphorylase (GMP) activity.

Main Methods:

• Comparative analysis of protein sequences to identify conserved motifs.
• Structural and functional characterization of PMI types I and II.
• Enzyme activity assays for both PMI and GMP activities.

Main Results:

• A conserved protein motif was identified in both PMI types I and II.
• This motif was found to coincide with the catalytic site of Candida albicans type I PMI.
• Type II PMI demonstrated bifunctional activity, possessing both PMI and GMP enzymatic functions within separate domains.

Conclusions:

• PMI types I and II likely share a common catalytic mechanism due to the conserved motif.
• The identified motif serves as a key functional element in the catalytic process of PMI.
• Type II PMI represents a versatile enzyme with dual catalytic capabilities, potentially functioning as separate enzymes in some species.