T1 - Regulation of proline biosynthesis

Pyrroline-5-carboxylate reductase (PYCR) is the final enzyme in proline biosynthesis, catalyzing the NAD(P)H-dependent reduction of Δ1-pyrroline-5-carboxylate (P5C) to proline. Mutations in the PYCR1 gene alter mitochondrial function and cause the connective tissue disorder cutis laxa. Furthermore, PYCR1 is overexpressed in multiple cancers, and the PYCR1 knock-out suppresses tumorigenic growth, suggesting that PYCR1 is a potential cancer target. However, inhibitor development has been stymied by limited mechanistic details for the enzyme, particularly in light of a previous crystallographic study that placed the cofactor-binding site in the C-terminal domain rather than the anticipated Rossmann fold of the N-terminal domain. To fill this gap, we report crystallographic, sedimentation-velocity, and kinetics data for human PYCR1. Structures of binary complexes of PYCR1 with NADPH or proline determined at 1.9 Å resolution provide insight into cofactor and substrate recognition. We see NADPH bound to the Rossmann fold, over 25 Å from the previously proposed site. The 1.85 Å resolution structure of a ternary complex containing NADPH and a P5C/proline analog provides a model of the Michaelis complex formed during hydride transfer. Sedimentation velocity shows that PYCR1 forms a concentration-dependent decamer in solution, consistent with the pentamer-of-dimers assembly seen crystallographically. Kinetic and mutational analysis confirmed several features seen in the crystal structure, including the importance of a hydrogen bond between Thr-238 and the substrate as well as limited cofactor discrimination.

MetaCyc L-proline biosynthesis III

Proline: Biosynthesis, Regulation and Health Benefits

is the final enzyme in proline biosynthesis…

Histidine is special in that its biosynthesis is inherently linked to thepathways of nucleotide formation. Histidine residues are often found in enzymeactive sites, where the chemistry of the imidazole ring of histidine makes it anucleophile and a good acid/base catalyzer. We now know that RNA can havecatalytic properties, and there has been speculation that life was originallyRNA-based. Perhaps the transition to protein catalysis from RNA catalysisoccurred at the origin of histidine biosynthesis.

The proline biosynthesis in living organisms | SpringerLink

We will look at this pathway in a bit more detail, because it involves themolecule 5-phosphoribosyl--pyrophosphate (which wewill refer to as "PRPP" from now on). PRPP is also involved in thesynthesis of purines and pyrimidines, as we will soon see. In the first step ofhistidine synthesis, PRPP condenses with ATP to form a purine, N1-5'-phosphoribosylATP, in a reaction that is driven by the subsequent hydrolysis of thepyrophosphate that condenses out. Glutamine again plays a role as an amino groupdonor, this time resulting in the formation of 5-aminoamidazole-4-carboximideribonucleotide (ACAIR), which is an intermediate in purine biosynthesis.

The significance of endproduct inhibition of proline biosynthesis and of compartmentation in relation to stress-induced proline accumulation
Much of this recent progress has been made possible by advances in our knowledge of the enzymes and genes involved in proline biosynthesis in man.

Proline biosynthesis in Saccharomyces cerevisiae: analysis of ..

So, the synthesis of asparagine is intrinsically tied to that of glutamine,and it turns out that glutamine is the amino group donor in the formation ofnumerous biosynthetic products, as well as being a storage form of NH3. Therefore, one would expect that glutamine synthetase, the enzyme responsiblefor the amidation of glutamate, plays a central role in the regulation ofnitrogen metabolism. We will now look into this control in more detail, beforeproceeding to the biosynthesis of the remaining nonessential amino acids.

Human Salivary Acidic Proline-rich Protein Polymorphisms and Biosynthesis Studied by High …

The proline biosynthesis in living organisms, Amino …

Pérez-Arellano, I., Carmona-Álvarez, F., Martínez, A. I., Rodríguez-Díaz, J. and Cervera, J. (2010), Pyrroline-5-carboxylate synthase and proline biosynthesis: From osmotolerance to rare metabolic disease. Protein Science, 19: 372–382. doi: 10.1002/pro.340

Loss of function of Pro1 significantly inhibits proline biosynthesis and ..

Pathway Commons::citrulline biosynthesis

N2 - Δ1-pyrroline-5-carboxylate synthase (P5CS), a bifunctional ATP- and NADPH-dependent mitochondrial enzyme, catalyzes the reduction of glutamate to Δ1-pyrroline-5-carboxylate, a critical step in the biosynthesis of proline, ornithine and arginine. Recently, we reported the cloning and expression of human and murine P5CS cDNAs. Previously, we showed that mammalian P5CS undergoes alternative splicing to generate two isoforms differing only by a 2 amino acid insert at the N-terminus of the γ-glutamyl kinase active site. The short isoform has high activity in the gut, where it participates in arginine biosynthesis and is inhibited by ornithine. The long isoform, expressed in multiple tissues, is necessary for the synthesis of proline from glutamate and is insensitive to ornithine. Here, we describe a newly recognized inborn error due to the deficiency of P5CS in two siblings with progressive neurodegeneration, joint laxity, skin hyperelasticity and bilateral subcapsular cataracts. Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia. Both are homozygous for the missense mutation, R84Q, which alters a conserved residue in the P5CS γ-glutamyl kinase domain. R84Q is not present in 194 control chromosomes and dramatically reduces the activity of both P5CS isoforms when expressed in mammalian cells. Additionally, R84Q appears to destabilize the long isoform. This is the first documented report of an inborn error of P5CS and suggests that this disorder should be considered in the differential diagnosis in patients with neurodegeneration and/or cataracts and connective tissue disease.