Tetrapeptide inhibitors of the glutamate vesicular transporter (VGLUT)

Abstract

Quinoline-2,4-dicarboxylic acids (QDCs) bearing lipophilic substituents in the 6- or 7-position were shown to be inhibitors of the glutamate vesicular transporter (VGLUT). Using the arrangement of the QDC lipophilic substituents as a template, libraries of X(1)X(2)EF and X(1)X(2)EW tetrapeptides were synthesized and tested as VGLUT inhibitors. The peptides QIEW and WNEF were found to be the most potent. Further stereochemical deconvolution of these two peptides showed dQlIdElW to be the best inhibitor (K(i)=828+/-252 microM). Modeling and overlay of the tetrapeptide inhibitors with the existing pharmacophore showed that H-bonding and lipophilic residues are important for VGLUT binding.

Fig 1

Structures of VGLUT inhibitors

Fig 2

Proposed QDC inhibitor structural relationship to peptides.

Fig. 3

Tetrapeptide design based on the QDC-template.

Fig 4

Demonstration of the inhibitory dose-response dependency of dQlIdElW on the uptake of ³H-l-glutamate (0.25 mM) into rat brain synaptic vesicles. Representative plot yielded a K_i = 0.465 mM. The control rate for L-glutamate uptake was 1912 nmol/min/mg protein and K_m = 2.1 mM.

Fig. 5

An extended conformation of the tetrapeptide lQdIlEdW (green) aligned in relation to a computationally-derived VGLUT superposition pharmacophore model composed with QDC (grey), one half of CSB (yellow) and BCP (orange), in which the ligands are correlated together with defined common pharmacophore comparison points (γ-carboxyl group, H-bonding acceptor and lipophilic pocket). Inter-atomic distances noted.

Scheme 1

Synthesis of target tetrapeptides containing a glutamate at position 3.