Yasutsugu Shimonishi

Carboxyl methylation and farnesylation of transducin gamma-subunit synergistically enhance its coupling with metarhodopsin II.

A heterotrimeric G‐protein in vertebrate photoreceptor cells is called transducin (T alpha beta gamma), whose gamma‐subunit is a mixture of two components, T gamma‐1 and T gamma‐2. T gamma‐2 is S‐farnesylated and partly carboxyl methylated at the C‐terminal cysteine residue, whereas T gamma‐1 lacks the modified cysteine residue. To elucidate the physiological significance of the double modifications in T gamma, we established a simple chromatographic procedure to isolate T gamma‐1, methylated T gamma‐2 and non‐methylated T gamma‐2 on a reversed phase column. Taking advantage of the high and reproducible yield of T gamma from the column, we analyzed the composition of T gamma subspecies in the T alpha‐T beta gamma complex which did not bind with transducin‐depleted rod outer segment membranes containing metarhodopsin II. The binding of T alpha‐T beta gamma with the membranes was shown to require the S‐farnesylated cysteine residue of T gamma, whose methylation further enhanced the binding. This synergistic effect was not evident when T alpha was either absent or converted to the GTP‐bound form which is known to dissociate from T beta gamma. Thus we concluded that a formation of the ternary complex, T alpha‐T beta gamma‐metarhodopsin II, is enhanced by the farnesylation and methylation of T gamma. This suggests that the double modifications provide most efficient signal transduction in photoreceptor cells.

Structure of IgE epitopes on a new 39-kD allergen molecule from the house dust mite, Dermatophagoides farinae

Two IgE epitope sequences comprising Ser56-Pro-Val-Thr-Lys-Arg-Ala-Ser-Leu-Lys-Ile-Asp-Ser-Lys-Lys70 and Asp104-Val-Glu-Leu-Ser-Leu-Arg-Ser-Ser-Asp-Ile-Ala115 were identified by deletion analysis of the cDNA encoding a new 39-kD protein of mite allergen. A synthetic dodecapeptide corresponding to the latter epitope sequence functioned as a monovalent and mite-specific hapten. Replacement of each of the 12 amino acid residues with Gly, using site-directed mutagenesis, indicated that Arg110 may play a central role in IgE binding. However, the 8 allergic sera tested exhibited a wide variation in their amino acid residues required for reactivity to IgE in allergic sera.

A Novel Modification of the Lysine Residue at Position 12 of Histone H4 in Starfish Sperm.

Post-translational modification of core histones is essential in processes requiring chromatin remodeling. We report here a novel modification in histones of the sperm of the starfish, Asterina pectinifera, which involves an ε-(γ-glutamyl)lysine cross-link between the glutamine residue at position 9 of histone H2B and the lysine residue at position 12 of histone H4.