O-phosphohomoserine, a naturally occurring analogue of phosphonate amino acid antagonists, is an N-methyl-D-aspartate (NMDA) antagonist in rat hippocampus

Synthesis of Phospho-Amino Acid Analogues as Tissue Adhesive Cement Additives

In this paper we report the synthesis of a library of phospho-amino acid analogues, via a novel single-step allyl-phosphoester protection/Pd-mediated deprotection strategy. These phosphoserine and phosphotyrosine analogues were then applied as additives to create adhesive calcium phosphate cements, allowing us to probe the chemical origins of the increased surface binding strength. We demonstrate the importance of multiple calcium binding motifs in mediating adhesion, as well as highlighting the crucial role played by substrate hydrophobicity and orientation in controlling binding strength.

A threonine synthase homolog from a mammalian genome

The genomes of several vertebrates contain two genes encoding proteins highly similar to threonine synthase (TS), even though the biosynthesis of l-threonine (l-Thr) is not known to occur in these animals. We report a bioinformatic analysis of the two TS-like genes, the recombinant expression of one murine TS homolog (mTSH2) and its initial biochemical characterization. Recombinant mTSH2 contained bound pyridoxal-5'-phosphate (PLP), but did not synthesize l-Thr. The enzyme did, however, bind O-phospho-homoserine (PHS; the actual TS substrate) and degraded it to alpha-ketobutyrate, phosphate, and ammonia-a known side reaction of microbial TSs. mTSH2 also degraded O-phospho-threonine (PThr) to alpha-ketobutyrate, showing that it can act as a catabolic phospho-lyase on both gamma- and beta-phosphorylated substrates. These findings suggest an unusual evolutionary origin for mTSH2, whereby an original TS enzyme became 'recycled' into a phospho-lyase upon dismissal, in metazoa, of the l-Thr biosynthetic pathway.

Sulfate esters of hydroxy amino acids as stereospecific glutamate receptor agonists

Enantiomerically pure sulfate esters of the hydroxy amino acids homoserine, hydroxyproline and 4-hydroxypipecolic acid were synthesized and tested on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors present in the mice cortical wedge preparation and on NMDA receptors present in the myenteric plexus of the guinea pig with the aim of finding new possible endogenous ligands (either agonists or antagonists) for excitatory amino acid receptors. The linear and flexible compound S-homoserine sulfate caused a depolarization of both AMPA and NMDA receptors. In the cortex its agonist action had an EC50 of 150 microM for NMDA and 300 microM for AMPA receptors and in the myenteric plexus its EC50 was 600 microM. The stereoisomer R-homoserine sulfate did not depolarize the cortical wedges and failed to cause ileal contraction up to a concentration of 500 microM. Among the four possible stereoisomers of 4-hydroxyproline sulfate, which are rigid structures and may be regarded as cyclization forms of homoserine sulfate, t-S-hydroxyproline sulfate was a selective AMPA receptor agonist with an EC50 of 70 microM in the cortex. The other three isomers were not active as agonists up to 500 microM and none of them had antagonist activity. Finally, t-4-hydroxy-S-pipecolic acid-4-sulfate, a superior homologue of t-S-hydroxyproline sulfate, was found to be one of the most potent and selective NMDA receptor agonists so far described with an EC50 of 0.7 microM in the cortex and 250 microM in the myenteric plexus.(ABSTRACT TRUNCATED AT 250 WORDS)