PDBsum entry 4l65

Transferase

PDB id: 4l65

Contents

Protein chain

750 a.a.

Ligands

C2F

MET

Metals

_ZN

Waters ×137

References listed in PDB file

Key reference

• Title: Structural analysis of a fungal methionine synthase with substrates and inhibitors.
• Authors: D.Ubhi, G.Kago, A.F.Monzingo, J.D.Robertus.
• Ref.: J Mol Biol, 2014, 426, 1839-1847. [DOI no: 10.1016/j.jmb.2014.02.006]
• PubMed id: 24524835

Abstract

The cobalamin-independent methionine synthase from Candida albicans, known as Met6p, is a 90-kDa enzyme that consists of two (βα)8 barrels. The active site is located between the two domains and has binding sites for a zinc ion and substrates l-homocysteine and 5-methyl-tetrahydrofolate-glutamate3. Met6p catalyzes transfer of the methyl group of 5-methyl-tetrahydrofolate-glutamate3 to the l-homocysteine thiolate to generate methionine. Met6p is essential for fungal growth, and we currently pursue it as an antifungal drug design target. Here we report the binding of l-homocysteine, methionine, and several folate analogs. We show that binding of l-homocysteine or methionine results in conformational rearrangements at the amino acid binding pocket, moving the catalytic zinc into position to activate the thiol group. We also map the folate binding pocket and identify specific binding residues, like Asn126, whose mutation eliminates catalytic activity. We also report the development of a robust fluorescence-based activity assay suitable for high-throughput screening. We use this assay and an X-ray structure to characterize methotrexate as a weak inhibitor of fungal Met6p.