In order to understand the fluid nature of biomembrane, which plays crucially important role in many aspects of life phenomena, the molecular motion of phospholipid and membrane protein is discussed in this review. It is shown that the primary determinant for the fluidity in the lipid bilayer and the rate for diffusive motion of lipid and protein molecules is the width and rate of wobbling motion of phospholipid acyl-chain in the nanosecond time region. For the lateral and rotational diffusion rate of membrane proteins, however, interaction between protein and cytoskeleton is also important as the secondary determinant. The rate of segmental motion of protein is partly governed by the surrounding phospholipid species, suggesting that specific phospholipids support the optimum conditions in protein structure to develop its action.
Consequently, the term “membrane fluidity” is complex conception having a hirarchical structure which consists of lipid and protein molecules.

抄録全体を表示

Membranes of foreign material are generally highly susceptible to the host complement system, which is a major humoral host defense system. Via the binding of the complement effector, C3, and C9, to the membranes, foreign cells are damaged by a variety of chemical and physical reactions induced by the host immune system. We have found that two membrane proteins classified into short consensus repeat (SCR) protein family, namely CD46 and CD55, are crucial to determine the complement susceptibility of membranes : that is, host cells circumvent autologous complement attack by the expression of either CD46 or CD55, whilst foreign cells are killed by host complement because of their lack of them. In this review, we discuss 1) the molecular mechanism of the membrane deposition of C3 and C9, and the interaction between these effector molecules and inhibitor molecules including CD46 and CD55 (which occur on membranes), 2) the alteration of membrane itself induced by complement attack, 3) the intracellular events (including signal transduction) evoked secondary to complement activation.

抄録全体を表示

E-cadherin (uvomorulin) is a member of the Ca²⁺-dependent cell adhesion molecules (cadherins). Its cytoplasmic region complexes with structurally distinct proteins termed α-, β-, and γ-catenins. cDNA cloning has revealed that α-catenin is a vinculin homologue whereas β-catenin is closely related to plakoglobin. A specific recognition site for catenins has been located in a carboxyl-terminal 72 amino acid domain (the catenin-binding domain). The association with catenins is of crucial importance for the cell adhesion function of E-cadherin, since mutant E-cadherins with deletions in the catenin-binding domain show no activity in cell aggregation assays. A cell line, which express E-cadherin and catenins except for α-catenin, shows poor adhesiveness but transfection of cDNA for αN-catenin, a subtype of α-catenin, results in an increased adhessiveness of the cells. A combination of biochemical analyses on the molecular organization of the E-cadherin-catenin complex has shown that a single complex is composed of one molecule of E-cadherin, one molecule of α-catenin, and one molecule of β-catenin. β-catenin has been shown to interact directly with E-cadherin. In pulse-chase experiments β-catenin is already associated with the 135 kD E-cadherin precursor molecule but the assembly of the newly synthesized α-, and γ-catenin into the complex is only detected around the time of endoproteolytic processing. Transformation of cells with v-src results in tyrosine phosphorylation of the cadherin-catenin complex and perturbed cadherin-mediated cell adhesion whereas a tyrosine kinase inhibitor revertes the effect of transformation. These results suggest a possible role of the tyrosine phosphorylation of the complex in regulating cadherin function.

抄録全体を表示

Heterotrimeric GTP-binding proteins (G proteins) consisting of α, β and γ subunitis play an crucial role in transmission of extracellular signals to effectors through membrane-bound receptors. Existence of many subtypes of effector enzymes, in addition to a number of G protein isoforms, makes it complicate to understand mechanisms of signal transduction. Recently, it has been demonstrated that each subtype of effectors, such as adenylyl cyclase and phosphoinositide-specific phospholipase C, is differently regulated by α and/or β γ subunits of distinct G proteins. In this review, structure and function of heterotrimeric GTP-binding proteins regulating effectors are summarized.

抄録全体を表示

The carbohydrate-binding domain of Bauhinia purpurea lectin (BPA), a galactose and lactose-binding lectin, was investigated from Asp-N endoproteinase digests of BPA. A peptide which interacted with lactose was purified by means of lactose-Sepharose column chromatography. It consisted of 9 amino acids and its amino acid sequence was DTWPNTEWS. The chemical synthesis of this nonapeptide was carried out by the solid-phase method and the synthetic peptide was found to exhibit lac-tose-specific binding activity in the presence of calcium. Similar studies were carried out on several anti-H (O) lectins and the peptides which showed affinity were also found as a part of the metal-binding region of these lectins. Subsequently, we constructed a chimeric lectin gene in which nonapeptide sequence was replaced by the corresponding region of the mannose-binding Lens culinaris lectin. The chimeric lectin expressed in E. coli was found to bind α-mannosyl-bovine serum albumin. These results are the first to describe the presence of a “variable-binding region” in legume lectins that detemine their carbohydrate-binding specificity

抄録全体を表示

A new system for the separation of organic vapor in mixture gas has been commercialized using the membrane separation process. The system is applied to the process of vapor recovery, gas purification, and other gas separation

抄録全体を表示