A Preliminary Study Of A New Mammalian Protein Synthesis Correction Mechanism Hdtd

It has been thought that D-amino acids were excluded from living systems except for D-amino acids in the cell wall of microorganisms. However, D-amino acids, in the form of free amino acids, peptides and proteins, were recently detected in various living organisms from bacteria to mammals. Regional high concentration of D-serine exists in mammal brain. D-serine is an internal ligand for N-methyl-D-Aspartate (NMDA) receptor, which updated traditional concept of "neurotransmitters". This is a new target for some acute and chronic neurological diseases due to up- or down-regulation of NMDA receptors. Increased concentrations of D-amino acids are relative to Alzheimer's disease (AD). There are amounts of D-aspartate in β amyloidal peptide separated from neurofibrillary tangles and neuritic plaque. Racemation of Asp²³ in Aβ accelerated its precipitation. All these data suggest that the un-correct incorporation of D-amino acids is an important factor in the pathogenesis of neurodegenerative diseases.Full-length cDNA of HDTD was cloned from human 3-month fetal brain library. Its full length is 1219bp, containing an open reading frame encoding 209 amino acids. The ATG at the position of 48-50 was predicted as the start codon because the sequence around the potential translation initiation conformed well to the consensus sequence of Kozat. HDTD is well homologous to D-Tyr-tRNA^Tyr deacylases of E.coli, yeast and Hemophilias influenza. The identity with DTD of E.coli is 39%, with that of yeast is 47%. These orthologs share a common DTyr-deacylase domain.Northern blot hybridization under high stringency condition revealed HDTD has one transcript of 1.3kb. The tissue expression pattern of HDTD mRNA appeared as relatively high levels in brain and testis, which was in good agreement with the regional high concentration of D-amino acids in human tissues. pET28a-HDTD recombinant protein was prokaryoticly expressed and purified in E. coli. At the same time, pET30a-TyrRS recombinant protein was prokaryoticly expressed and purified in E. coli. Human tRNA^Try was prepared by transcription in vitro. The activity of HDTD protein was demonstrated by capillary electrophoresis.It was reported that D-serine is an endogenous ligand for the glycine site of the...