Inhibition of the action of the stimulatory GDP/GTP exchange protein for smg p21 by the geranylgeranylated synthetic peptides designed from its C-terminal region

smg p21B, a member of the ras p21-like small GTP-binding protein superfamily, undergoes post-translational modifications, which are geranylgeranylation of the cysteine residue in the C-terminal region followed by removal of the three C-terminal amino acids (QLL) and the subsequent carboxyl methylation of the exposed prenylated cysteine residue. smg p21B has a polybasic region upstream of the prenylated cysteine residue. We have previously proposed that these C-terminal structures of smg p21B are essential for the action of its stimulatory GDP/GTP exchange protein, named GDP dissociation stimulator (GDS). We studied here which structure of the C-terminal region of smg p21B is important for its interaction with smg p21 GDS. For this purpose, we synthesized a peptide according to the C-terminal structure of smg p21B, which was PGKARKKSSC-geranylgeranyl-carboxyl methyl, and its variously modified peptides and examined their ability to interact with smg p21 GDS and to interfere with the smg p21 GDS action to stimulate the GDP/GTP exchange reaction of smg p21B. The results indicate that the phosphorylated form of PGKARKKSSC-geranylgeranyl stoichiometrically interacts with smg p21 GDS, that the presence of the geranylgeranyl moiety is essential for, but not sufficient for, the smg p21 GDS action, and that the presence of the methyl moiety, removal of the three C-terminal amino acids, and the presence of the polybasic amino acids also affect the smg p21 GDS action. It is likely that all the steps of the post-translational processing and presence of the polybasic region in the C-terminal region of smg p21B are related to its interaction with smg p21 GDS.     

Purification method for α-1-acid glycoprotein with subsequent high-performance liquid chromatographic determination of monosaccharides in plasma of healthy subjects and patients with renal insufficiency

A simple purification method for human plasma α-1-acid glycoprotein (AAG) using an ion-exchange and hydroxyapatite column was developed. The recovery of the method was found to be high. We also improved a determination method for N-acetylneuraminic acid and monosaccharides in the carbohydrate moiety of AAG by using an ion-exchange column and pulse-amperometric detection. By this method, a composition analysis of the carbohydrate moiety of AAG (N-acetylneuraminic acid, fucose, N-acetyl glucosamine, galactose and mannose) was possible with 1.0 ml of plasma. We compared these carbohydrate concentrations in the AAG of patients with renal insufficiency with those of healthy subjects. In the AAG of the patients, the concentrations of N-acetylglucosamine, galactose and mannose were significantly higher than those in the AAG of the healthy subjects.