Molecular structure of human galactose mutarotase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Galactose mutarotase (EC 5.1.3.3) facilitates the interconversion of alpha- and beta-D-galactose, essential for normal galactose metabolism.
• This enzyme is ubiquitously found in various organisms, including bacteria, plants, and animals, and resides in the cytoplasm.

Purpose of the Study:

• To elucidate the three-dimensional structure of human galactose mutarotase using X-ray crystallography.
• To investigate the enzyme's active site and substrate-binding interactions in both apo and substrate-bound forms.

Main Methods:

• X-ray crystallographic analysis of human galactose mutarotase in its apoform and complexed with beta-D-galactose.
• Determination of the protein's molecular architecture, including secondary and tertiary structural elements.

Main Results:

• The crystal structure reveals a complex fold comprising 29 beta-strands, 25 reverse turns, and 2 alpha-helices.
• The substrate, beta-D-galactose, binds in a shallow cleft, interacting with key residues including Glu-307 (catalytic base) and His-176 (catalytic acid).
• Comparison with bacterial and C. elegans galactose mutarotases highlights structural differences in loop regions connecting beta-strands.

Conclusions:

• The identified catalytic residues (Glu-307 and His-176) are conserved across species, suggesting a conserved catalytic mechanism.
• Structural variations in loop regions may contribute to differences in enzyme activity or regulation among species.
• This structural information provides a foundation for understanding galactose metabolism and potential therapeutic interventions.