Heterozygous Beta thalassemia: balanced globin synthesis in bone marrow cells

In two patients with heterozygous beta thalassemia the rates of synthesis of the alpha and beta chains of hemoglobin were equal in nucleated red cell precursors, although beta chain synthesis was reduced in peripheral blood reticulocytes. This finding suggests a relative instability of beta chain messenger RNA in beta thalassemia.     

Multiple mutations produce delta beta 0 thalassemia in Sardinia

In Sardinia the common form of beta thalassemia is a beta 0 thalassemia due to a nonsense mutation at codon 39. delta beta 0 Thalassemia is rare in Sardinia and is associated with increased production of hemoglobin F of the A gamma type. In this study we used a synthetic oligomer assay and detected the beta 39 nonsense mutation on the delta beta 0 thalassemia chromosome. Hence at least two different mutations have occurred on this chromosome; one that increases A gamma globin synthesis and another that silences the beta globin gene.     

Silent hemoglobin alpha genes in apes: potential source of thalassemia

Small quantities of unusual hemoglobins were found in 1 of 37 chimpanzees and 2 of 6 gorillas. In each genus these hemoglobins contain unique alpha chains that differ from the ordinary by eight to nine scattered amino acid changes. The unusual chains arise from a hitherto undetected hemoglobin (3)alpha locus. No (3)alpha products are found in most apes; accordingly, (3)alpha is considered synthetically inactive in all but a few reversion mutants. Indirect evidence that the inactive (3)alpha locus is juxtaposed to an active alpha locus together with the supposition that (3)alpha exists in man provides a setting wherein thalassemia might be produced by nonhomologous recombination between two loci.     

Rabbit hemoglobin biosynthesis: use of human hemoglobin chains to study molecule completion

A cell-free protein-synthesizing system made from rabbit reticulocytes was used to incorporate (14)C-amino acids into hemoglobin. Electrophoretic analyses of the soluble products of this cell-free system revealed a fraction containing rabbit (14)C-alpha chains in addition to the rabbit (14)C-hemoglobin. The addition of isolated human hemoglobin beta chains to this system during active synthesis inhibited the release of newly synthesized rabbit (14)C-beta chains into solution from the ribosome fraction. This inhibition was possibly a result of hybrid hemoglobin formation between rabbit alpha and human beta chains. A model of hemoglobin construction in which soluble alpha chains are intermediates is suggested. These alpha chains may aid in the release of beta chains from the polyribosomes during the completion of the hemoglobin molecule.     

Evolution of a protein fold in vitro

A "switch" mutant of the Arc repressor homodimer was constructed by interchanging the sequence positions of a hydrophobic core residue, leucine 12, and an adjacent surface polar residue, asparagine 11, in each strand of an intersubunit beta sheet. The mutant protein adopts a fold in which each beta strand is replaced by a right-handed helix and side chains in this region undergo significant repacking. The observed structural changes allow the protein to maintain solvent exposure of polar side chains and optimal burial of hydrophobic side chains. These results suggest that new protein folds can evolve from existing folds without drastic or large-scale mutagenesis.     

Tertiary structure of plant RuBisCO: domains and their contacts

The three-dimensional structure of ribulose-1,5-biphosphate carboxylase-oxygenase (RuBisCO), has been determined at 2.6 A resolution. This enzyme initiates photosynthesis by combining carbon dioxide with ribulose bisphosphate to form two molecules of 3-phosphoglycerate. In plants, RuBisCO is built from eight large (L) and eight small (S) polypeptide chains, or subunits. Both S chains and the NH2-terminal domain (N) of L are antiparallel beta, "open-face-sandwich" domains with four-stranded beta sheets and flanking alpha helices. The main domain (B) of L is an alpha/beta barrel containing most of the catalytic residues. The active site is in a pocket at the opening of the barrel that is partly covered by the N domain of a neighboring L chain. The domain contacts of the molecule and its conserved residues are discussed in terms of this structure.     

新生儿脐血红细胞平均体积和红细胞平均血红蛋白对地中海贫血初筛的探讨

目的 :探讨新生儿脐血红细胞平均体积 (MCV)和红细胞平均血红蛋白 (MCH)与地中海贫血的关系。方法 :用血细胞计数仪测定新生儿脐血的MCV和MCH ,用醋酸纤维薄膜电泳检测脐血的HbBart’s,用跨越断裂点PCR(gap PCR)法检测东南亚缺失型α 地中海贫血 1基因。结果 :地中海贫血组的新生儿脐血MCV和MCH明显小于正常新生儿组 (P <0 .0 1) ,符合小细胞低色素性贫血。结论 :新生儿脐血的MCV和MCH可为地中海贫血的临床诊断提供依据     

Correction of murine beta-thalassemia by gene transfer into the germ line

A murine beta-thalassemia was corrected by the transfer of cloned beta-globin genes into the mouse germ line. The cloned mouse beta maj-globin gene or the cloned human beta-globin gene was introduced into mice deficient in beta-globin synthesis because of a deletion of the beta maj-globin gene. Both introduced genes produced functional beta-globin chains, leading to a reduction in one case, and elimination in another case, of the anemia and associated abnormalities of the red blood cells.     

Location of gene for beta subunit of human T-cell receptor at band 7q35, a region prone to rearrangements in T cells

The T-cell receptor is formed by two chains, alpha and beta, for which specific clones were recently obtained. In this report the gene for the beta chain of the human T-cell receptor was located on the long arm of chromosome 7, band q35, by means of in situ hybridization. This chromosome region in T cells is unusually prone to develop breaks in vivo, perhaps reflecting instability generated by somatic rearrangement of T-cell receptor genes during normal differentiation in this cell lineage.     

The role of beta 2-microglobulin in peptide binding by class I molecules

Efficient transport of class I major histocompatibility complex molecules to the cell surface requires association of the class I heavy chain with endogenous peptide and the class I light chain, beta 2-microglobulin (beta 2M). A mutant cell line deficient in beta 2M transports low amounts of nonpeptide-associated heavy chains to the cell surface that can associate with exogenously provided beta 2M and synthetic peptide antigens. Normal beta 2M-sufficient cells grown in serum-free media devoid of beta 2M also require an exogenous source of beta 2M to efficiently bind synthetic peptide. Thus, class I molecules on normal cells do not spontaneously bind or exchange peptides.     

Functional expression of a cloned I-A beta k gene in B-lymphoma cells

The immune response genes of the mouse encode two cell-surface glycoproteins, I-A and I-E, that play critical roles in determining the animal's immune responsiveness. The I-A antigen contains two chains, alpha and beta. A cloned beta-chain gene, I-A beta k, was introduced into B-lymphoma cells that express I-Ad. The transfected gene was successfully expressed on the cell surface of the recipient cells and was functional in stimulating allospecific T cells.     

Atomic structure of thymidylate synthase: target for rational drug design

The atomic structure of thymidylate synthase from Lactobacillus casei was determined at 3 angstrom resolution. The native enzyme is a dimer of identical subunits. The dimer interface is formed by an unusual association between five-stranded beta sheets present in each monomer. Comparison of known sequences with the Lactobacillus casei structure suggests that they all have a common core structure around which loops are inserted or deleted in different sequences. Residues from both subunits contribute to each active site. Two arginine side chains can contribute to binding phosphate on the substrate. The side chains of several conserved amino acids can account for other determinants of substrate binding.     

Isotypic exclusion of gamma delta T cell receptors in transgenic mice bearing a rearranged beta-chain gene

The rearrangement of T cell antigen receptor beta- and gamma-chain gene segments was studied in transgenic mice that bear a functional beta-chain gene. Virtually all CD3-positive T cells derived from transgenic mice express beta chains containing the transgene-encoded V beta 8.2 variable region on their surfaces and do not express endogenous beta-chain variable regions. Expression of endogenous V beta genes is inhibited at the level of somatic recombination during thymic ontogeny. Furthermore, rearrangements of the TCR gamma-chain genes are also markedly inhibited in these transgenic animals. Hence expression of the TCR beta transgene has led to allelic exclusion of alpha beta receptors and isotypic exclusion of gamma delta T cell receptors.     

HEL cells: a new human erythroleukemia cell line with spontaneous and induced globin expression

A new human erythroleukemia cell line has been established. This line, designated HEL, is capable of spontaneous and induced globin synthesis, producing mainly G gamma and A gamma chains. Embryonic chains (epsilon, zeta) and alpha chains are detectable in very small amounts; beta chains are undetectable. This line provides a new model system for studying aspects of erythroid cell differentiation and differential globin gene expression.     

Murine I-A beta chain polymorphism: nucleotide sequences of three allelic I-A beta genes

The polymorphism of immune response genes plays a critical role in determining the immune capabilities of a particular individual. The molecular nature of this polymorphism was studied by examining the structure of the coding portions of three alleles of the I-A beta chain gene, an immune response gene whose protein product constitutes a subunit of the I-A molecule. Comparison of the I-A beta chains encoded by these alleles revealed an amino acid sequence divergence of 5 to 8 percent. The differences were found to be a series of short alterations clustered in the amino terminal half of the polypeptide.     

绿竹与毛竹纤维素合成酶(CesA)的生物信息学分析

纤维素是竹细胞壁的主要组成成份,其存在形式--小微纤丝是由纤维素合成酶(CesA)催化作用得到的36根β-1,4糖苷链结晶而成.以GeneBank数据库中已登陆的完整竹类蛋白序列为分析对象,对其进行系统进化、物理性质、跨膜结构和二级结构的生物信息学分析.结果表明:(1)绿竹和毛竹CesA与水稻CesA具有较高同源性;(...     

Differences in collagen metabolism between normal and osteoarthritic human articular cartilage

Normal human articular cartilage synthesizes only one type of a chain, which exhibits the chromatographic behavior of the alpha(l)(II) chains described for chick and bovine cartilage. Osteoarthritic cartilage, on the other hand, synthesizes in addition a collagen containing alpha(2) chains and beta components. The different structural features of the two types of collagen may account for some of the functional defects of osteoarthritic cartilage.     

A novel, highly stable fold of the immunoglobulin binding domain of streptococcal protein G

The high-resolution three-dimensional structure of a single immunoglobulin binding domain (B1, which comprises 56 residues including the NH2-terminal Met) of protein G from group G Streptococcus has been determined in solution by nuclear magnetic resonance spectroscopy on the basis of 1058 experimental restraints. The average atomic root-mean-square distribution about the mean coordinate positions is 0.27 angstrom (A) for the backbone atoms, 0.65 A for all atoms, and 0.39 A for atoms excluding disordered surface side chains. The structure has no disulfide bridges and is composed of a four-stranded beta sheet, on top of which lies a long helix. The central two strands (beta 1 and beta 4), comprising the NH2- and COOH-termini, are parallel, and the outer two strands (beta 2 and beta 3) are connected by the helix in a +3x crossover. This novel topology (-1, +3x, -1), coupled with an extensive hydrogen-bonding network and a tightly packed and buried hydrophobic core, is probably responsible for the extreme thermal stability of this small domain (reversible melting at 87 degrees C).     

Structure of fungal fatty acid synthase and implications for iterative substrate shuttling

We report crystal structures of the 2.6-megadalton alpha6beta6 heterododecameric fatty acid synthase from Thermomyces lanuginosus at 3.1 angstrom resolution. The alpha and beta polypeptide chains form the six catalytic domains required for fatty acid synthesis and numerous expansion segments responsible for extensive intersubunit connections. Detailed views of all active sites provide insights into substrate specificities and catalytic mechanisms and reveal their unique characteristics, which are due to the integration into the multienzyme. The mode of acyl carrier protein attachment in the reaction chamber, together with the spatial distribution of active sites, suggests that iterative substrate shuttling is achieved by a relatively restricted circular motion of the carrier domain in the multifunctional enzyme.     

Single chain alkali resistance in hemoglobin Rainier: beta 145 tyrosine-histidine

The mechanism of alkali resistance in hemoglobin Rainier, an adult human hemoglobin variant (beta 145 tyrosinie --> histidinie), has been investigated. Alkali denaturation kinetics, electrophoretic and hybridization study. and ultracentrifuge analysis provided evidence for a monomeric beta Rainiier chain resisting denaturation at alkaline pH. These data provide evidence for a previously unrecognized effect of a single amino acid substitution, that is, the change of the alkali denaturation properties of monomneric chains.