The structure of Medicago truncatula δ1-pyrroline-5-carboxylate reductase provides new insights into regulation of proline biosynthesis in plants

Abstract

The two pathways for proline biosynthesis in higher plants share the last step, the conversion of δ1-pyrroline-5-carboxylate (P5C) to L-proline, which is catalyzed by P5C reductase (P5CR, EC 1.5.1.2) with the use of NAD(P)H as a coenzyme. There is increasing amount of evidence to suggest a complex regulation of P5CR activity at the post-translational level, yet the molecular basis of these mechanisms is unknown. Here we report the three-dimensional structure of the P5CR enzyme from the model legume Medicago truncatula (Mt). The crystal structures of unliganded MtP5CR decamer, and its complexes with the products NAD+, NADP+, and L-proline were refined using x-ray diffraction data (at 1.7, 1.85, 1.95, and 2.1 Å resolution, respectively). Based on the presented structural data, the coenzyme preference for NADPH over NADH was explained, and NADPH is suggested to be the only coenzyme used by MtP5CR in vivo. Furthermore, the insensitivity of MtP5CR to feed-back inhibition by proline, revealed by enzymatic analysis, was correlated with structural features. Additionally, a mechanism for the modulation of enzyme activity by chloride anions is discussed, as well as the rationale for the possible development of effective enzyme inhibitors.

Structural Studies of Medicago truncatula Histidinol Phosphate Phosphatase from Inositol Monophosphatase Superfamily Reveal Details of Penultimate Step of Histidine Biosynthesis in Plants

“…7A) possibly act as claws that recruit HOLP (by its phosphate group) and guide the substrate at the initial phase of binding. A similar behavior of two Lys residues, surrounding the entrance to the active site, was proposed for NADP(H) binding to M. truncatula ␦1-pyrroline-5-carboxylate reductase (59).…”

Resolving the cofactor-binding site in the proline biosynthetic enzyme human pyrroline-5-carboxylate reductase 1

“…The P5CR decamer has been described in detail elsewhere, so only a summary is provided here (14,15,17). The decamer is a pentamer-of-dimers assembly that resembles an "hourglassshaped barrel" (14) when viewed perpendicular to the 5-fold axis (Fig.…”

Lysine metabolism and amino acid profile in maize grains from plants subjected to cadmium exposure

“…In this sense, enhancements in AK sensitivity to Lys feedback inhibition ( Figure 3; Table 4) may stimulate Pro accumulation ( Figure 6) through avoidance of high Lys production. A second hypothesis was originated from the discovery that pyrroline-5-carboxylate reductase -PC5R, which is the enzyme that catalyzes the final step of Pro synthesis, is stimulated by chloride anions at low concentrations (Ruszkowski et al, 2015).…”