The reference OMIM entry for this protein is 610936

Phosphoserine aminotransferase 1; psat1
Psat
Endometrial progesterone-induced protein; epip

DESCRIPTION

L-serine serves as a building block for protein synthesis and can be modified in different metabolic pathways to generate several essential compounds. Although it is available from dietary sources, L-serine can be synthesized from 3-phosphoglycerate via 3 enzymatic steps in the phosphorylated pathway. PSAT (EC 2.6.1.52) catalyzes the second step in the pathway, conversion of 3-phosphohydroxypyruvate into 3-phosphoserine (Baek et al., 2003).

CLONING

Baek et al. (2003) cloned 2 PSAT1 splice variants, which they called PSAT-alpha and -beta, from a human Jurkat T-cell cDNA library. The full-length PSAT-beta transcript encodes a deduced 370-amino acid protein with a calculated molecular mass of 40 kD. PSAT-alpha lacks exon 8 and encodes a deduced 324-amino acid protein with a calculated molecular mass of 35.2 kD. Compared with PSAT-beta, PSAT-alpha lacks 46 amino acids. Both proteins contain a conserved binding domain for the cofactor pyridoxal 5-prime-phosphate (vitamin B6). PSAT-beta shares 92.4% amino acid similarity with its mouse homolog. PSAT-beta orthologs were present in all species examined, including plants, insects, and bacteria. Northern blot analysis detected highest expression of a 2.2-kb transcript in brain, liver, kidney, and pancreas, with weaker expression in thymus, prostate, testis, and colon. No expression was detected in spleen, ovary, small intestine, peripheral blood mononuclear cells, heart, placenta, lung, and skeletal muscle. RT-PCR detected both variants in all human cell lines examined, and PSAT-beta was always the more abundant form. Western blot analysis detected the 40-kD PSAT-beta protein in all human cell lines examined, whereas the 32.5-kD PSAT-alpha protein was only weakly expressed in hepatoma and chronic myelogenous leukemia cell lines. The level of PSAT-beta protein was proportional to the amount of PSAT-beta mRNA detected in these cell lines.

GENE FUNCTION

Using Northern blot analysis, Misrahi et al. (1987) showed that Psat, which they called Epip, was upregulated in a dose-dependent manner by progesterone and more weakly by estradiol in rabbit endometrium. Progesterone and estradiol inhibitors decreased the elicited Psat expression. PSAT mRNA was detected in human endometrium during the luteal phase, but not during the follicular phase or during pregnancy. Baek et al. (2003) found that enzymatic activity of recombinant PSAT-beta was nearly 7 times higher than that of PSAT-alpha, which showed barely detectable activity. Both PSAT-alpha and -beta could rescue deletion of their S. cerevisiae counterpart. Northern blot analysis of synchronized Jurkat T cells showed that expression of PSAT reached a maximum in S phase and decreased to basal levels as cells moved to the G2/M boundary.

GENE STRUCTURE

Baek et al. (2003) determined that the PSAT gene contains 9 exons and spans 56 kb.

MOLECULAR GENETICS

- Phosphoserine Aminotransferase Deficiency Hart et al. (2007) identified PSAT deficiency (PSATD; 610992) in a brother and sister who showed low concentrations of serine and glycine in plasma and cerebrospinal fluid. The index patient presented with intractable seizures, acquired microcephaly, hypertonia, and psychomotor retardation and died at age 7 months despite supplementation with serine and glycine from age 11 weeks. His sister received treatment from birth, which led to a normal outcome at age 3 years. Measurement of PSAT1 activity in cult ... More on the omim web site

Subscribe to this protein entry history

Nov. 17, 2018: Protein entry updated
Automatic update: OMIM entry 610936 was added.

Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).