Dihydrofolate reductase: x-ray structure of the binary complex with methotrexate

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Dihydrofolate reductase (DHFR) is a crucial enzyme in folate metabolism.
• Its polypeptide backbone folding involves a central eight-stranded beta-pleated sheet.
• Structural similarities exist between DHFR and dinucleotide binding domains of dehydrogenases.

Purpose of the Study:

• To elucidate the structural characteristics of dihydrofolate reductase.
• To investigate the binding interactions of methotrexate within the enzyme's active site.
• To compare the folding patterns of DHFR with related enzyme domains.

Main Methods:

• Analysis of the polypeptide backbone folding in dihydrofolate reductase.
• Geometric comparison of DHFR's beta-pleated sheet and helices with dinucleotide binding domains.
• Examination of methotrexate binding within the enzyme's cavity.

Main Results:

• The central eight-stranded beta-pleated sheet is a key structural feature of DHFR.
• DHFR's innermost four strands and two bridging helices share geometric similarity with dinucleotide binding domains but differ in connectivity.
• Methotrexate binds in a deep cavity, with its pteridine ring in a hydrophobic pocket, and forms a strong interaction with aspartic acid 27.

Conclusions:

• The unique folding of DHFR contributes to its function.
• Structural comparisons reveal evolutionary relationships and functional adaptations in enzyme families.
• Specific interactions between aspartic acid 27 and methotrexate highlight key binding determinants for enzyme inhibition.