Predisposition of genetic disease by modestly decreased expression of GCH1 mutant allele

Recently it was shown that single nucleotide polymorphisms (SNPs) can explain individual variation because of the small changes of the gene expression level and that the 50% decreased expression of an allele might even lead to predisposition to cancer. In this study, we found that a decreased expression of an allele might cause predisposition to genetic disease. Dopa responsive dystonia (DRD) is a dominant disease caused by mutations in GCH1 gene. The sequence analysis of the GCH1 in a patient with typical DRD symptoms revealed two novel missense mutations instead of a single dominant mutation. Family members with either of the mutations did not have any symptoms of DRD. The expression level of a R198W mutant allele decreased to about 50%, suggesting that modestly decreased expression caused by an SNP should lead to predisposition of a genetic disease in susceptible individuals.

Transient phosphorylation of tumor associated microtubule associated protein (TMAP)/cytoskeleton associated protein 2 (CKAP2) at Thr-596 during early phases of mitosis

Tumor associated microtubule associated protein (TMAP), also known as cytoskeleton associated protein 2 (CKAP2) is a mitotic spindle-associated protein whose expression is cell cycle-regulated and also frequently deregulated in cancer cells. Two monoclonal antibodies (mAbs) against TMAP/CKAP2 were produced: B-1-13 and D-12-3. Interestingly, the reactivity of mAb D-12-3 to TMAP/CKAP2 was markedly decreased specifically in mitotic cell lysate. The epitope mapping study showed that mAb D-12-3 recognizes the amino acid sequence between 569 and 625 and that phosphorylation at T596 completely abolishes the reactivity of the antibody, suggesting that the differential reactivity originates from the phosphorylation status at T596. Immunofluorescence staining showed that mAb D-12-3 fails to detect TMAP/CKAP2 in mitotic cells between prophase and metaphase, but the staining becomes evident again in anaphase, suggesting that phosphorylation at T596 occurs transiently during early phases of mitosis. These results suggest that the cellular functions of TMAP/CKAP2 might be regulated by timely phosphorylation and dephosphorylation during the course of mitosis.

Increased lysine N-methylation of a 23-kDa protein during hepatic regeneration

The methylation of a 23-kDa nuclear protein increased after partial hepatectomy and methylation returned to basal levels after the initial stage of regeneration. The methylating enzyme was partially purified from rat liver by ammonium sulfate precipitation, DEAE-anion exchange chromatography and Butyl-Sepharose chromatography. The 23-kDa protein was purified from a nuclear fraction of liver tissue with SP-Sepharose. When the 23-kDa protein was methylated with the partially purified methyltransferase and analyzed on C18 high performance liquid chromatography (HPLC), the methylated acceptor amino acid was monomethyl lysine (MML). Previously, only arginine N-methylation of specific substrate proteins has been reported during liver regeneration. However, in this report, we found that lysine N-methylation increased during early hepatic regeneration, suggesting that lysine N-methylation of the 23-kDa nuclear protein may play a functional role in hepatic regeneration. The methyltransferase did not methylate other proteins such as histones, hnRNPA1, or cytochrome C, suggesting the enzyme is a 23-kDa nuclear protein- specific lysine N-methyltransferase.

A Family with A Missense Mutation in the SCN5A Gene

Brugada syndrome, an autosomal dominantly inherited form of ventricular fibrillation, is characterized by ST-segment elevation in leads V1-3 and right bundle-branch block on surface electrocardiogram. It is caused by mutations in the cardiac sodium channel gene, SCN5A, and to the best of our knowledge, there has been no report of this mutation in Korea. Three members of a family were heterozygous for a G to T substitution at the nucleotide position 5851 in exon 28 of the SCN5A gene. This nucleotide alteration makes a missense mutation, leading to a valine to leucine substitution (V1951L), in the carboxy terminal region of the sodium channel a subunit. We report here a missense mutation in a Korean family with Brugada-type electrocardiogram.

Cysteine carboxyl O-methylation of human placental 23 kDa protein

C-Terminal carboxyl methylation of a human placental 23 kDa protein catalyzed by membrane-associated methyltransferase has been investigated. The 23 kDa protein substrate methylated was partially purified by DEAE-Sephacel, hydroxyapatite and Sephadex G-100 gel filtration chromatographies. The substrate protein was eluted on Sephadex G-100 gel filtration chromatography as a protein of about 29 kDa. In the absence of Mg2+, the methylation was stimulated by guanine nucleotides (GTP, GDP and GTPgammaS), but in the presence of Mg2+, only GTPgammaS stimulated the methylation which was similar to the effect on the G25K/rhoGDI complex. AFC, an inhibitor of C-terminal carboxyl methylation, inhibited the methylation of human placental 23 kDa protein. These results suggests that the substrate is a small G protein different from the G25K and is methylated on C-terminal isoprenylated cysteine residue. This was also confirmed by vapor phase analysis. The methylated substrate protein was redistributed to membrane after in vitro methylation, suggesting that the methylation of this protein is important for the redistribution of the 23 kDa small G protein for its putative role in intracellular signaling.