The distribution and relative immunogenicity of calf alpha-crystallin antigenic determinants on different subunits.

In the native alpha-crystallin molecule, 45.9% of all reactive antigenic determinants were found to be located on SH-containing subunits. Of these, the majority (35.3%) were reaggregation dependent, and 10.6% were reactive on monomeric subunits. By contrast, only 10.9% of all antigenic determinants were located on SH-free subunits, and the ratio of aggregation-dependent determinants (4.4%) to those of monomeric subunits (6.5%) was reversed compared to SH-containing subunits. Among all antigenic determinants reactive in native alpha-crystallin, 44.1% were dependent on the presence of both types of subunits. These data indicate that the antigenic determinants requiring subunit interaction were formed from SH-containing and SH-free subunits in a ratio of 1:1. Direct analysis showed that in the alpha-crystallin molecule, the ratio of these subunits is 2:1. The experiments indicate that some conformations of subunits in the native molecule persist in separated subunits. The relative immunogenicity of each type of antigenic determinant expressed as the ratio of the percentage of the determinant reactive in the native calf lens alpha-crystallin to the percentage of corresponding antibodies induced by native alpha-crystallin was found to be close to 1.     

Deficiency of subunits in heart mitochondrial NADH-ubiquinone oxidoreductase of a patient with mitochondrial encephalomyopathy and cardiomyopathy

The heart mitochondria isolated from a patient with hypertrophic cardiomyopathy associated with mitochondrial encephalomyopathy were analyzed by immunoblotting using specific antibody against each of the purified mitochondrial energy transducing complexes from beef heart. Subunits of NADH-ubiquinone oxidoreductase (Complex I) were markedly decreased and those of cytochrome c oxidase (Complex IV) were decreased to some extent, but the deficiency of any of these subunits was only partial. On the other hand, the contents of subunits of ubiquinol-cytochrome c oxidoreductase (Complex III) were normal. These results suggest that the decreased levels of some of the Complex I subunits might be the primary cause of disorder in this patient.     

The nuclear encoded subunits of complex I from bovine heart mitochondria

NADH:ubiquinone oxidoreductase (complex I) from bovine heart mitochondria is a complicated, multi-subunit, membrane-bound assembly. Recently, the subunit compositions of complex I and three of its subcomplexes have been reevaluated comprehensively. The subunits were fractionated by three independent methods, each based on a different property of the subunits. Forty-six different subunits, with a combined molecular mass of 980 kDa, were identified. The three subcomplexes, Iα, Iβ and Iλ, correlate with parts of the membrane extrinsic and membrane-bound domains of the complex. Therefore, the partitioning of subunits amongst these subcomplexes has provided information about their arrangement within the L-shaped structure. The sequences of 45 subunits of complex I have been determined. Seven of them are encoded by mitochondrial DNA, and 38 are products of the nuclear genome, imported into the mitochondrion from the cytoplasm. Post-translational modifications of many of the nuclear encoded subunits of complex I have been identified. The seven mitochondrially encoded subunits, and seven of the nuclear encoded subunits, are homologues of the 14 subunits found in prokaryotic complexes I. They are considered to be sufficient for energy transduction by complex I, and they are known as the core subunits. The core subunits bind a flavin mononucleotide (FMN) at the active site for NADH oxidation, up to eight iron-sulfur clusters, and one or more ubiquinone molecules. The locations of some of the cofactors can be inferred from the sequences of the core subunits. The remaining 31 subunits of bovine complex I are the supernumerary subunits, which may be important either for the stability of the complex, or for its assembly. Sequence relationships suggest that some of them carry out reactions unrelated to the NADH:ubiquinone oxidoreductase activity of the complex.     

Impact of ageing on proteasome structure and function in human lymphocytes

Key actors of the immune response, lymphocytes exhibit functional deficits with advancing age. For instance, the age-related decline in lymphocyte proliferation may be related to alteration in the degradation of crucial proteins such as cell-cycle regulators. Degradation of these proteins is mediated by the ubiquitin-26S proteasome system. The proteasome is also the major "housekeeping" proteolytic complex responsible for eliminating intracellular damaged proteins. To investigate the occurrence of proteasome structural and functional age-related alterations, 26S proteasome was purified from peripheral blood lymphocytes of 20-63-year-old donors. Changes in peptidase activity were measured and modifications in the proteasome particle structure were analysed using bi-dimensional electrophoresis. We found the age-related decline of 26S proteasome-specific activity to be associated with an increased yield of post-translational modifications of proteasome subunits, while proteasome content and subunit composition were unchanged. In particular, some catalytic and assembly subunits of the 20S proteasome were preferentially modified with age. Western blotting of proteasome subunits resolved by bi-dimensional electrophoresis showed some of these modified subunits to be glycated, conjugated with a lipid peroxidation product and/or ubiquitinated. In conclusion, it is suggested that structural alterations of proteasome subunits may contribute to the observed decline of proteasome activity with age and could play a major role in immune senescence.     

Renal gamma-glutamyl transpeptidases: structural and immunological studies

Mammalian kidney gamma-glutamyl transpeptidases are compared with respect to subunit size, amino-terminal sequences of the two subunits, immunological, and some catalytic properties. The species-related variation in the apparent molecular weight of the subunits has been shown to be primarily due to the extent and nature of protein glycosylation. Using antibodies raised against the native enzymes and isolated sodium dodecyl sulfate-treated subunits, it is shown that the transpeptidases share some antigenic determinants. Some of these determinants in the highly glycosylated transpeptidase subunits can be detected by the antibodies only upon deglycosylation of the subunits. The amino-terminal sequences of the subunits exhibit considerable homology, in agreement with the immunological data. Thus, there are two segments of identity (3 and 5 residues in length, respectively) in the first 17 amino-terminal residues of the heavy subunits of rat, bovine, dog, and human kidney transpeptidases (papain-solubilized). Of particular interest is the finding of 91 to 96% identity in the first 23 amino-terminal residues of the small subunit of these transpeptidases. The small subunit contains the gamma-glutamyl binding site of the enzyme. There are three segments of identity (7, 6, and 8 residues in length, respectively) in the first 23 residues, each separated by either a Ser or an Ala residue. The first 7 amino-terminal residues of the small subunit in all four species are identical, indicating a high degree of specificity in the proteolytic processing of the common, single-chain precursor of the two subunits. Differences noted between transpeptidases in their relative acceptor specificity and in their susceptibility to inactivation by the glutamine antagonist, AT-125 (acivicin), must reflect subtle structural differences in their active center domains.     

The nuclear encoded subunits of complex I from bovine heart mitochondria

NADH:ubiquinone oxidoreductase (complex I) from bovine heart mitochondria is a complicated, multi-subunit, membrane-bound assembly. Recently, the subunit compositions of complex I and three of its subcomplexes have been reevaluated comprehensively. The subunits were fractionated by three independent methods, each based on a different property of the subunits. Forty-six different subunits, with a combined molecular mass of 980 kDa, were identified. The three subcomplexes, I alpha, I beta and I lambda, correlate with parts of the membrane extrinsic and membrane-bound domains of the complex. Therefore, the partitioning of subunits amongst these subcomplexes has provided information about their arrangement within the L-shaped structure. The sequences of 45 subunits of complex I have been determined. Seven of them are encoded by mitochondrial DNA, and 38 are products of the nuclear genome, imported into the mitochondrion from the cytoplasm. Post-translational modifications of many of the nuclear encoded subunits of complex I have been identified. The seven mitochondrially encoded subunits, and seven of the nuclear encoded subunits, are homologues of the 14 subunits found in prokaryotic complexes I. They are considered to be sufficient for energy transduction by complex I, and they are known as the core subunits. The core subunits bind a flavin mononucleotide (FMN) at the active site for NADH oxidation, up to eight iron-sulfur clusters, and one or more ubiquinone molecules. The locations of some of the cofactors can be inferred from the sequences of the core subunits. The remaining 31 subunits of bovine complex I are the supernumerary subunits, which may be important either for the stability of the complex, or for its assembly. Sequence relationships suggest that some of them carry out reactions unrelated to the NADH:ubiquinone oxidoreductase activity of the complex.     

Biosynthesis of mitochondrial membrane proteins: Co-ordination with special reference to cytochrome c oxidase

Summary This paper reviews mechanisms by which the rate of synthesis of subunits of mitochondrial inner membrane protein complexes and the assembly of these subunits are co-ordinated. Current models are evaluated and critically discussed in the light of some recent evidences. The focus is on the incorporation of cytoplasmically-synthesized cytochrome c oxidase subunits in the development of a newer model, which introduces some twists into a combination of several current ideas. A mechanism which governs both organized assembly and the co-ordination of rates of polypeptide synthesis is illustrated and the principles of the model are applied to the elucidation of some odd features of certain mutants. The possibilities that mitochondrial ATPase and cytochrome c reductase may also be synthesized and assembled according to this model are discussed.     

Subunits of human condensins are potential therapeutic targets for cancers

The main role of condensins is to regulate chromosome condensation and segregation during cell cycles. Recently, it has been suggested in the literatures that subunits of condensin I and condensin II are involved in some human cancers. This paper will first briefly discuss discoveries of human condensins, their components and structures, and their multiple cellular functions. This will be followed by reviews of most recent studies on subunits of human condensins and their dysregulations or mutations in human cancers. It can be concluded that many of these subunits have potentials to be novel targets for cancer therapies. However, hCAP-D2, a subunit of human condensin I, has not been directly documented to be associated with any human cancers to date. This review hypothesizes that hCAP-D2 can also be a potential therapeutic target for human cancers, and therefore that all subunits of human condensins are potential therapeutic targets for human cancers.     

Intracellular contents and assembly states of all 12 subunits of the RNA polymerase II in the fission yeast Schizosaccharomyces pombe.

The RNA polymerase II (Pol II) of the fission yeast Schizosaccharomyces pombe is composed of 12 different polypeptides, Rpb1 to Rpb12, of which five, Rpb5, Rpb6, Rpb8, Rpb10 and Rpb12, are shared among three forms of the RNA polymerase. To get an insight into the control of synthesis and assembly of individual subunits, we have measured the intracellular concentrations of all 12 subunits in S. pombe by quantitative immunoblotting. Results indicate that the levels are low for the three large subunits, Rpb1, Rpb2 and Rpb3, which are the homologues of beta', beta and alpha subunits, respectively, of prokaryotic RNA polymerase. On the other hand, the levels of small-sized subunits were between 2- to 15-fold higher than these three core subunits. The levels of the five common subunits shared among RNA polymerases I, II and III are about 10 times greater than those of the Pol II-specific core subunits. The assembly state of the Rpb proteins was analyzed by glycerol gradient centrifugation of S. pombe whole cell extracts. The three core subunits are mostly assembled in Pol II, but some of the small subunits were detected in the slowly sedimenting fractions, indicating that at least some of the excess Rpb proteins exist in unassembled forms. Based on the intracellular concentration of the least abundant Rpb3 subunit, the total number of Pol II in a growing S. pombe cell was estimated to be about 10,000 molecules. The intracellular distribution of some Pol II subunits was also analyzed by microscopic observation of the green fluorescent protein (GFP)-fused Rpb proteins. In agreement with the biochemical analysis, the GFP-Rpb1 and GFP-Rpb3 fusions were present in the nuclei but the GFP-Rpb4 was detected in the cytoplasm as well as the nuclei.     

The effects of fasting, diabetes, and hypophysectomy on adipose lactic dehydrogenase isozymes.

Lactic dehydrogenase isozyme distributions have been examined in epididymal adipose tissue of fasting, diabetic, and hypophysectomized rats. In each of these conditions the electrophoresis patterns show an enhancement of H subunits relative to M subunits suggestive of an induction of H subunits. Careful assessment of the total lactic dehydrogenase activity of adipose tissue from fasted, diabetic, and hypophysectomized rats reveals, however, that these conditions decrease total lactic dehydrogenase activity to approximately one-half those of normal animals. When this factor and the relative activity of the M and H subunits are taken into consideration it is apparent that the pattern shift from normal in these three states is due to a disproportionate loss of M subunits. An explanation for these shifts is that some degradative process, possibly activation of a protease, is induced by each of these stress conditions which selectively degrades M subunits. An interesting reversal by phosphate of the electrophoresis patterns of fasting, hypophysectomized, and diabetic rats is demonstrated.     

Identification and localization of G-proteins in the clonal adipocyte cell lines HGFu and Ob17

HGFu and Ob17 are cell lines derived from adipose tissue of lean (+/?) and ob/ob mice, respectively. Neither adenylyl cyclase activity nor G protein abundance and subcellular distribution have been assessed previously in these cells. Cyclase activity was low and resistant to catecholamine stimulation in both cell lines. However, the enzyme could be stimulated to high levels by forskolin and Mn²⁺. G_sα (largely the long isoform), G_iα2, and Gβ were the major G protein subunits identified. The levels of G protein mRNA expression were similar in both cell lines and, unlike actin expression, did not change as a result of differentiation. Immunoblotting and ADP-ribosylation of the G peptides corroborated these results. Assessment of the subcellular localization of the subunits by indirect epifluorescence and scanning confocal microscopy showed that each of the subunits had a characteristic subcellular pattern. G_sα showed vesicular cytoplasmic and nuclear staining; G_iα2 colocalized with actin stress fibers and disruption of these structures altered the distribution of G_iα2; β subunits showed some colocalization with the stress fibers as well as a cytoplasmic vesicular and nuclear pattern. As a result of differentiation, there was reorganization of the actin, together with the G_iα2 and β fibrous patterns. Both cell lines showed similar modifications. The induction of differentiation in these cells is therefore not associated with changes in adenylyl cyclase activity nor of the abundance of G-protein subunits, although reorganization of some of these subunits does accompany actin reorganization.     

The NDUFB6 subunit of the mitochondrial respiratory chain complex I is required for electron transfer activity: A proof of principle study on stable and controlled RNA interference in human cell lines

Molecular bases of inherited deficiencies of mitochondrial respiratory chain complex I are still unknown in a high proportion of patients. Among 45 subunits making up this large complex, more than half has unknown function(s). Understanding the function of these subunits would contribute to our knowledge on mitochondrial physiology but might also reveal that some of these subunits are not required for the catalytic activity of the complex. A direct consequence of this finding would be the reduction of the number of candidate genes to be sequenced in patients with decreased complex I activity. In this study, we tested two different methods to stably extinct complex I subunits in cultured cells. We first found that lentivirus-mediated shRNA expression frequently resulted in the unpredicted extinction of additional gene(s) beside targeted ones. This can be ascribed to uncontrolled genetic material insertions in the genome of the host cell. This approach thus appeared inappropriate to study unknown functions of a gene. Next, we found it possible to specifically extinct a CI subunit gene by direct insertion of a miR targeting CI subunits in a Flp site (HEK293 Flp-In cells). By using this strategy we unambiguously demonstrated that the NDUFB6 subunit is required for complex I activity, and defined conditions suitable to undertake a systematic and stable extinction of the different supernumerary subunits in human cells.     

Properties and modifications of a cryomacroglobulin possessing cold agglutinin activity

The physical properties of a pathological γ^M-globulin with cold agglutinin activity and cryoglobulin solubility could be modified by changes in temperature and pH and upon dilution. The type of changes noted appear to simulate those expected in a readily dissociable antigen-antibody complex. Naturally occurring and chemically produced subunits of the γ^M-globulin and Fc-fragments of myeloma proteins diminished the cryoproperty of the γ^M-globulin and effected changes in its physical properties but did not alter its cold agglutinin activity. Cryoglobulin properties could be conferred upon some purified γ^M-globulins by reacting them with Fc-fragments. Mercaptan dissociation of the Cryomacroglobulin produces subunits with loss of the noted activities. Reaggregation of these subunits restores some of the native properties, but variable results which are dependent on the type of mercaptan employed are obtained. Attempts to explain the cold agglutinin activity of γ^M-globulin hybrids containing variable amounts of mercaptan-produced active and inert subunits suggest that activity requires two of the five subunits to be derived from the γ^M-cold agglutinin and to be adjacent to each other.     

Shaker, Shal, Shab, and Shaw express independent K+ current systems.

Although many K+ channel genes encoding homologous subunits have been cloned, a central question remains: how do these subunits associate to produce the diversity of K+ currents observed in living cells? Previous work has shown that different subunits encoded by the Shaker gene subfamily are able to form heteromultimers, which add to the diversity of currents. However, the unrestrained mixing of subunits from all genes to form hybrid channels would be undesirable for some cells that clearly require functionally discrete K+ currents. We show that Drosophila Shaker, Shal, Shab, and Shaw subunits form functional homomultimers, but that a molecular barrier to heteropolymerization is present. Coexpression of all four K+ channel systems does not alter their individual properties in any way. These experiments also demonstrate that multiple, independent A-current systems together with multiple, independent delayed rectifier systems can coexist in single cells.     

Evolution of glutamine amidotransferase genes. Nucleotide sequences of the pabA genes from Salmonella typhimurium, Klebsiella aerogenes and Serratia marcescens

The amide group of glutamine is a source of nitrogen in the biosynthesis of a variety of compounds. These reactions are catalyzed by a group of enzymes known as glutamine amidotransferases; two of these, the glutamine amidotransferase subunits of p-aminobenzoate synthase and anthranilate synthase have been studied in detail and have been shown to be structurally and functionally related. In some micro-organisms, p-aminobenzoate synthase and anthranilate synthase share a common glutamine amidotransferase subunit. We report here the primary DNA and deduced amino acid sequences of the p-aminobenzoate synthase glutamine amidotransferase subunits from Salmonella typhimurium, Klebsiella aerogenes and Serratia marcescens. A comparison of these glutamine amidotransferase sequences to the sequences of ten others, including some that function specifically in either the p-aminobenzoate synthase or anthranilate synthase complexes and some that are shared by both synthase complexes, has revealed several interesting features of the structure and organization of these genes, and has allowed us to speculate as to the evolutionary history of this family of enzymes. We propose a model for the evolution of the p-aminobenzoate synthase and anthranilate synthase glutamine amidotransferase subunits in which the duplication and subsequent divergence of the genetic information encoding a shared glutamine amidotransferase subunit led to the evolution of two new pathway-specific enzymes.     

In Sickness and in Health: The Role of TRAPP and Associated Proteins in Disease

Transport protein particle (TRAPP) represents a series of related protein complexes that function in specific stages of inter‐organelle traffic. They share a core of subunits that can activate the GTPase Rab1 through a guanine nucleotide exchange factor (GEF) activity and are distinguished by ‘accessory’ subunits giving each complex its distinct function. The subunits are ubiquitously expressed and, thus, mutations in TRAPP subunits would be expected to be embryonic lethal. However, since its discovery, a number of subunits have been found to be mutated in several diverse human disorders suggesting that some of these subunits may have cell‐ or tissue‐specific functions. Here we review the current state of knowledge with respect to TRAPP subunit mutations in human disease. We suggest ideas to explain their tissue‐specific phenotypes and present avenues for future investigation.      

Subunit structure of anthranilate synthetase from Neurospora crassa.

Freshly purified preparations of anthranilate synthetase complex from Neurospora crassa appeared to be homogeneous on polyacrylamide disc gels and were composed of two distinct subunits, 94,000 and 70,000 daltons, respectively, as determined by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. Carboxymethylation of the complex or treatment with guanidine hydrochloride and urea before sodium dodecyl sulfate treatment did not alter the subunit pattern. When the purified complex was iodinated with 125I- or methylated with [14C]dimethylsulfate, no labeled components other than the two subunits stained with Coomassie blue were detected after electrophoresis in the presence of sodium dodecyl sulfate. Although some purified preparations were stable, most were unstable upon storage. Analysis of the unstable preparations on nondenaturing and sodium dodecyl sulfate polyacrylamide disc gels revealed that the complex in these preparations was progressively fragmented to smaller components and subunits upon repeated freeze-thaw treatment or prolonged incubation at or above 4 degrees. Distinct fragments were generated ranging in size down to 25,000 daltons, and some fragments retained some of the activities associated with the anthranilate synthetase complex. On the basis of these and earlier studies, we conclude that anthranilate synthetase from Neurospora crassa is composed of two distinct subunits in an alpha2beta2 structure; one subunit is a trifunctional peptide which contains the catalytic sites for the phosphoribosylanthranilate isomerase and indoleglycerol phosphate synthetase reactions, and associates with the second subunit to form glutamine-dependent anthranilate synthetase. The smaller subunits and components previously reported for this complex are apparently due to protease activity present in purified preparations.     

粘虫幼虫血淋巴中的凝集素

粘虫Mythlmna separata Walker幼虫血淋巴中含有凝集某些脊椎动物红细胞的凝集素,凝集活性可被乳糖、岩藻糖或神经氨酸抑制.用CNBr-sepharose 4B 进行亲和层析从血淋巴中分离的凝集素成分比较复杂,聚丙烯酰胺凝胶电泳显示三条区带,SDS聚丙烯酰胺凝胶电泳出现6个亚基,亚基分子量分别为71000、65000、56000、35000、33000及31000道尔顿.     

Heterogeneity of native ribosomal 60-S subunits in Ehrlich ascites tumor cells cultured in vitro.

Native large ribosomal subunits in cultured Ehrlich ascites tumor cells analyzed by high-resolution CsCl isopycnic centrifugation consist of at least two classes of particles with densities of 1.57 g/cm3 (LI) and 1.59 g/cm3 (LII), respectively. A wash with 0.5 M KCl converts LI into particles with the density of LII particles. Incubation of derived large subunits (density 1.59 g/cm3) with 0.5 M KCl wash of reticulocyte ribosomes leads to the formation of particles with the density of LI particles. A protein with a molecular weight of 57000 present in the high-KCl wash of 60-S native subunits was virtually absent in the KCl wash of 40-S subunits or polyribosomes suggesting that specific protein factors may be present on some native 60-S subunits. Possible functions of these protein factors are discussed.