Crystal structure-based selective targeting of the pyridoxal 5'-phosphate dependent enzyme kynurenine aminotransferase II for cognitive enhancement.

Fluctuations in the brain levels of the neuromodulator kynurenic acid may control cognitive processes and play a causative role in several catastrophic brain diseases. Elimination of the pyridoxal 5'-phosphate dependent enzyme kynurenine aminotransferase II reduces cerebral kynurenic acid synthesis and has procognitive effects. The present description of the crystal structure of human kynurenine aminotransferase II in complex with its potent and specific primary amine-bearing fluoroquinolone inhibitor (S)-(-)-9-(4-aminopiperazin-1-yl)-8-fluoro-3-methyl-6-oxo-2,3-dihydro-6H-1-oxa-3a-azaphenalene-5-carboxylic acid (BFF-122) should facilitate the structure-based development of cognition-enhancing drugs. From a medicinal chemistry perspective our results demonstrate that the issue of inhibitor specificity for highly conserved PLP-dependent enzymes could be successfully addressed.

Signal sequence and keyword trap in silico for selection of full-length human cDNAs encoding secretion or membrane proteins from oligo-capped cDNA libraries.

We have developed an in silico method of selection of human full-length cDNAs encoding secretion or membrane proteins from oligo-capped cDNA libraries. Fullness rates were increased to about 80% by combination of the oligo-capping method and ATGpr, software for prediction of translation start point and the coding potential. Then, using 5'-end single-pass sequences, cDNAs having the signal sequence were selected by PSORT ('signal sequence trap'). We also applied 'secretion or membrane protein-related keyword trap' based on the result of BLAST search against the SWISS-PROT database for the cDNAs which could not be selected by PSORT. Using the above procedures, 789 cDNAs were primarily selected and subjected to full-length sequencing, and 334 of these cDNAs were finally selected as novel. Most of the cDNAs (295 cDNAs: 88.3%) were predicted to encode secretion or membrane proteins. In particular, 165(80.5%) of the 205 cDNAs selected by PSORT were predicted to have signal sequences, while 70 (54.2%) of the 129 cDNAs selected by 'keyword trap' preserved the secretion or membrane protein-related keywords. Many important cDNAs were obtained, including transporters, receptors, and ligands, involved in significant cellular functions. Thus, an efficient method of selecting secretion or membrane protein-encoding cDNAs was developed by combining the above four procedures.

Function of ubiquitin-like domain of chicken 2'-5'-oligoadenylate synthetase in conformational stability.

2'-5'-Oligoadenylate synthetase (OAS), an interferon (IFN) induced enzyme, synthesizes 2'-5'-oligoadenylate (2-5A) from ATP when activated by dsRNA. Chicken OAS (ChOAS) has a ubiquitin-like (UbL) domain of two consecutive sequences (UbL1 and UbL2) at its carboxyl-terminus. The OAS gene has at least two alleles, OAS*A and OAS*B. OAS-A is the wild-type (wt) and OAS-B is a mutant deleted of a highly hydrophobic region of UbL1. To study the function of the UbL domain, enzymatic and physiologic properties were compared between OAS-A and OAS-B. OAS-B was more susceptible to trypsin than OAS-A and was converted very quickly into p38, deleting a greater part of the UbL domain. The p38 has the enzymatic activity to synthesize 2-5A. Thermal inactivation of OAS-B occurred at a lower temperature than that of OAS-A and p38, with loss of the ability to bind dsRNA. In contrast to OAS-A, the content of OAS-B in erythrocytes decreased during growth to a very low level. However, red blood cells (RBC) from anemic B/B chickens synthesized OAS-B at a high level comparable to A/A, although OAS-B levels decreased sharply again during maturation to erythrocytes. Thus, OAS-B carrying the mutated UbL domain is unstable compared with OAS-A in vitro and in vivo, and the wt UbL domain may contribute to the stability of the protein structure of ChOAS.

Protocadherin LKC, a new candidate for a tumor suppressor of colon and liver cancers, its association with contact inhibition of cell proliferation.

Protocadherins are a major subfamily of the cadherin superfamily, but little is known about their functions and intracellular signal transduction. We cloned a novel human protocadherin gene, containing seven EC domains, and identified functional aspects of this gene. The gene was predominantly expressed in liver, kidney and colon tissues, and was thus designated Protocadherin LKC. The expression of Protocadherin LKC is markedly reduced in cancers arising from these tissues at both transcriptional and protein levels. To investigate the effects of Protocadherin LKC expression in colon cancer, we introduced the gene into colon cancer cell line HCT116, which does not express this gene. Significantly, Protocadherin LKC expression induced contact inhibition of cell proliferation although it did not affect growth rate. When grown to post-confluence in monolayer cells cultures, Protocadherin LKC-expressing HCT116 no longer formed multiple cell layers and showed the typical paving stone morphology of normal epithelial cells. Furthermore, expression of Protocadherin LKC suppressed tumor formation of HCT116 cells in a nude mouse model. In addition, we identified a protein, hMAST205 (microtubule-associated serine/threonine kinase-205 kDa), which interacted with Protocadherin LKC; the interaction occurring between the PDZ domain of hMAST205 and C-terminal tail of Protocadherin LKC. Our results suggest that Protocadherin LKC, which directly binds PDZ protein, is a molecular switch for contact inhibition of epithelial cells in the liver, kidney and colon tissues.