Docking Studies and Ligand Recognition in Folylpolyglutamate Synthetase

Folylpolyglutamate synthetase (FPGS) catalyzes the sequential addition of several glutamates
to folate, forming γ-linked polyglutamate folates of varying lengths. To understand how this
protein is capable of accommodating ligands of different length and net charge, we have
performed docking studies for folate substrates and glutamate based on the ternary crystal
structure of Lactobacillus casei FPGS. Our results suggest two locations for folate binding,
the one seen in the crystal structure and another distinct cavity. According to our model and
experimental data, it is highly probable that folate can bind in both sites, and we suggest that
the new pocket is especially important for the initial addition of the first glutamate residue.
Docking longer substrates, di- and triglutamylated folates, showed how these molecules bind
in the same sites. The longer folates also adopted transition-state-like conformations that may
help us to understand the ligation reaction in FPGS and influence the design of mechanism-based inhibitors for anticancer or antimicrobial therapy.