L-Asp is a useful tool in the purification of the ionotropic glutamate receptor A2 ligand-binding domain

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Christian Krintel, Karla Frydenvang, Anna Ceravalls de Rabassa, Anne Mette Kaern, Michael Gajhede, Darryl S Pickering, Jette S Kastrup

In purification of the ionotropic glutamate receptor A2 (GluA2) ligand-binding domain (LBD), L-Glu supplemented buffers have previously been used for protein stabilization during the procedure. This sometimes hampers structural studies of low affinity ligands because L-Glu is difficult to displace despite extensive dialysis. Here, we show that L-Asp binds to full-length GluA2 with low affinity (Ki = 0.63 mM) and to GluA2 LBD with even lower affinity (Ki = 2.6 mM), and we use differential scanning differential scanning fluorimetry to show that L-Asp is able to stabilize the isolated GluA2 LBD. We also show that L-Asp can replace L-Glu during purification, providing both equal yields and purity of the resulting protein sample. Furthermore, we solved three structures of GluA2 LBD in the presence of 7.5 mM, 50 mM and 250 mM L-Asp, respectively. Surprisingly, with 7.5 mM L-Asp the GluA2 LBD crystallized as a mixed dimer with L-Glu present in one subunit while neither L-Asp nor L-Glu were found in the other subunit. Thus, residual L-Glu is still present from the expression. On the other hand, only L-Asp was found at the binding site when using 50 mM or 250 mM L-Asp for crystallization. The binding mode observed for L-Asp at the GluA2 LBD is very similar to that described for L-Glu. Taken together, we have shown that L-Asp can be used instead of L-Glu for ligand-dependent stabilization of the GluA2 LBD during purification. This will enable structural studies of low affinity ligands for lead optimization in structure-based drug design. This article is protected by copyright. All rights reserved.
Original languageEnglish
JournalF E B S Journal
Pages (from-to)2422–2430
Number of pages9
ISSN1742-464X
DOIs
Publication statusPublished - 27 Mar 2014

ID: 107359275