Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.2.1.23 (beta-galactosidase)
14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Numerous cell types, including fibroblasts, vascular smooth muscle cells, chondroblasts, monocytes, neutrophils, and several tumor cells express the 67-kD galactolectin, homologous to the alternatively spliced variant of beta-galactosidase. The 67-kD protein resides on the cell surfaces and is capable of interacting with elastin, laminin and collagen type IV. This peripheral membrane protein binds its matrix ligands but only in the absence of galactosugars, whereas binding of galactosugar-containing moieties to its lectin site changes its molecular folding which causes discharge of the ligand and release of the receptor from the cell surface. This review will address the functional significance of the single receptor that interacts with multiple matrix proteins and can be shed from cell surfaces by galactosugars. I will emphasize the role of the 67-kD protein in divergent cellular processes, such as cell-matrix attachment, matrix assembly, cellular chemotaxis, and active migration through the vascular walls.
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PMID:Nature and the multiple functions of the 67-kD elastin-/laminin binding protein. 782 55

The gene hoxN of Alcaligenes eutrophus encodes a membrane protein with a molecular mass of 33.1 kDa that mediates energy-dependent uptake of nickel ions. Based on the hydrophobicity of the HoxN protein five, six, or seven transmembrane segments were predicted, depending on the algorithm used for computer analysis. To distinguish between these possibilities varying segments of the amino-terminal end of the transporter were fused to the Escherichia coli enzymes alkaline phosphatase (PhoA) or beta-galactosidase (LacZ). The enzymatic activity of 16 HoxN-PhoA and 15 HoxN-LacZ fusions was determined. On the assumption that PhoA fusions only exhibit high activity when fused to periplasmic domains of the target, while LacZ fusions are only active when oriented towards the cytoplasm, a two-dimensional model for the nickel transporter was developed. This model proposes that HoxN contains four periplasmic and four cytoplasmic regions, and seven transmembrane helices. The amino terminus is located in the cytoplasm, and the carboxyl terminus faces the periplasm.
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PMID:A topological model for the high-affinity nickel transporter of Alcaligenes eutrophus. 793 94

Individual membrane protein spanning sequences can promote protein export. To help define the sequence features necessary for this action, we identified mutations disrupting export mediated by the first spanning sequence (TM1) of the Escherichia coli serine chemoreceptor. Mutant spanning sequences were generated and characterized using beta-galactosidase and alkaline phosphatase gene fusions. The protein export function of TM1 was remarkably tolerant of single charged residues, and the introduction of pairs of charged amino acids was necessary to eliminate export. The results are accommodated by a model in which export requires a stretch of uncharged residues whose summed hydrophobicity exceeds a particular threshold value. This threshold approximates the minimum hydrophobicity required for cleavable signal sequence function. In addition, the threshold was near the minimum hydrophobicity observed for wild-type spanning sequences in a collection of topologically characterized membrane proteins.
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PMID:Mutations eliminating the protein export function of a membrane-spanning sequence. 796 39

A set of low-copy-number vectors (pPD) has been constructed that permit selective gene expression and high-level protein overproduction in Escherichia coli, based on the bacteriophage T7 RNA polymerase/T7 promoter system. These plasmids carry a chloramphenicol resistance gene (cat) as a selective marker and an extended multiple cloning site for convenient gene cloning. Their replication is mediated by ori sequences derived from the low-copy-number vector pSC101. The efficient T7 gene 10 promoter present on these vectors allows selective and high-level transcription of cloned genes carrying their own translational initiation signals. In addition, low-copy-number T7 vectors were constructed that permit expression of genes lacking their own transcription and translation initiation elements by providing a ribosome binding site, an ATG start codon and a multiple cloning site devised for the cloning in all three reading frames. The pPD expression vectors were used to achieve high-level overproduction of the E. coli integral outer membrane protein Tsx, and the cytoplasmic enzymes beta-galactosidase (beta Gal) and UTP:alpha-D-glucose-1-phosphate uridylyltransferase (GalU). The characteristics of these low-copy-number T7 expression vectors should prove very useful for the cloning and high-level overexpression of genes whose gene products are deleterious to the E. coli host.
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PMID:Low-copy-number T7 vectors for selective gene expression and efficient protein overproduction in Escherichia coli. 798 88

The regulation of hutA, the Vibrio cholerae gene encoding a 77-kDa iron-regulated outer membrane protein required for heme iron utilization, was characterized, and the DNA sequence of the gene was determined. A hutA::Tn5 lac fusion generated previously (D. P. Henderson and S. M. Payne, Mol. Microbiol. 7:461-469, 1993) was transformed into Fur- and Fur+ strains of Escherichia coli and V. cholerae. The results of beta-galactosidase assays on the transformed strains demonstrated that transcription of hutA is regulated by the Fur repressor protein in E. coli and at least partially regulated by Fur in V. cholerae. Analysis of the DNA sequence of hutA indicated that a sequence homologous to the E. coli consensus Fur box was present in the promoter region of hutA. The amino acid sequence of HutA is homologous to those of several TonB-dependent outer member proteins. However, when the V. cholerae heme utilization system, which requires one or more genes encoded by the recombinant plasmid pHUT10 in addition to hutA carried on a second vector, was transferred to a wild-type strain and an isogenic tonB mutant of E. coli, the tonB mutant could utilize heme iron as efficiently as the wild-type strain. These data indicate that the V. cholerae heme utilization system reconstituted in E. coli does not require a functional TonB protein. The tonB mutant transformed with the heme utilization plasmids could not utilize the siderophore ferrichrome as an iron source, indicating that none of the genes encoded on the heme utilization plasmids complements the tonB defect in E. coli. It is possible that a gene(s) encoded by the recombinant heme utilization plasmids encodes a protein serving a TonB-like function in V. cholerae. A region in the carboxy terminus of HutA is homologous to the horse hemoglobin gamma chain, and the amino acids involved in forming the heme pocket in the gamma chain are conserved in HutA. These data suggest that this region of HutA is involved in heme binding.
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PMID:Characterization of the Vibrio cholerae outer membrane heme transport protein HutA: sequence of the gene, regulation of expression, and homology to the family of TonB-dependent proteins. 819 82

Photobacterium sp. strain SS9 is a deep-sea bacterium which modulates the abundances of several outer membrane proteins as a function of hydrostatic pressure. These proteins include the product of the previously cloned ompH gene (D. H. Bartlett, M. Wright, A. A. Yayanos, and M. Silverman. Nature (London) 342:572-574, 1989). Subsequent to conjugal plasmid delivery it was possible to cross an ompH::lacZ transcriptional fusion into the genome of SS9, replacing the wild-type ompH gene, generating strain EC10. EC10 is not impaired in growth at high pressure, indicating that under the growth conditions employed, OmpH is not required for baroadaptation. beta-Galactosidase production in EC10 is induced by high pressure to approximately the same extent that OmpH production is in the parental strain, SS9. Therefore, OmpH abundance appears to be primarily regulated at the transcriptional level. EC10 was used for the isolation of ompH regulatory mutants. Derivatives of EC10 which produce reduced levels of beta-galactosidase at both low and high pressure and which appeared to possess mutations outside the ompH::lacZ locus were obtained. All of these regulatory mutants displayed alterations in the high-pressure repression of a second outer membrane protein, designated OmpL, and two of the mutants were also deficient in the high-pressure induction of a third outer membrane protein, designated OmpI. The most dramatic phenotype was present in mutant EC1002, whose growth was extremely barosensitive. EC1002 is the first pressure-sensitive mutant ever isolated. Prolonged incubation of EC1002 at high pressure led to the accumulation of cells with wild-type growth characteristics at high pressure. These cells are suggested to possess suppressor mutations, as they remain deficient in beta-galactosidase production and maintain their high-pressure-adapted phenotype for many generations in the absence of high-pressure selection.
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PMID:Use of a reporter gene to follow high-pressure signal transduction in the deep-sea bacterium Photobacterium sp. strain SS9. 824 22

TolQ is a 230-amino-acid protein required to maintain the integrity of the bacterial envelope and to facilitate the import of both filamentous bacteriophage and group A colicins. Cellular fractionation experiments showed TolQ to be localized to the cytoplasmic membrane. Bacteria expressing a series of TolQ-beta-galactosidase and TolQ-alkaline phosphatase fusion proteins were analyzed for the appropriate enzyme activity, membrane location, and sensitivity to exogenously added protease. The results are consistent with TolQ being an integral cytoplasmic membrane protein with three membrane-spanning regions. The amino-terminal 19 residues as well as a small loop in the 155 to 170 residue region appear exposed in the periplasm, while the carboxy terminus and a large loop after the first transmembrane region are cytoplasmic. Amino-terminal sequence analysis of TolQ purified from the membrane revealed the presence of the initiating formyl methionine group, suggesting a rapid translocation of the amino-terminal region across the cytoplasmic membrane. Analysis of various tolQ mutant strains suggests that the third transmembrane region as well as parts of the large cytoplasmic loop are necessary for activity.
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PMID:Membrane topology and mutational analysis of the TolQ protein of Escherichia coli required for the uptake of macromolecules and cell envelope integrity. 830 May 35

The immunity protein (Imm) encoded by the Escherichia coli phage T4 effects exclusion of phage superinfecting cells already infected with T4. The 83-residue polypeptide possesses two long lipophilic areas (from residues 3 to 32 and 37 to 65) interrupted by a hydrophilic stretch including two positively charged residues. The charge distribution of the protein very strongly suggested that it is a plasma membrane protein with the C terminus facing the periplasm. While it could be shown that the expected location was correct, fusions of Imm to alkaline phosphatase or beta-galactosidase showed that the C terminus was at the cytosolic side of the membrane. Also, concerning function, there was almost no structural specificity to this part of the protein. Even removal of the two positively charged residues did not completely abolish function. Evidence suggesting that Imm is associated with the membrane at specific sites is presented. It is proposed that Imm is localized to the membrane with the help of a receptor and that, therefore, it does not follow the established rules for the topology of other membrane proteins. The results also suggest that Imm acts indirectly, possibly by altering the conformation of a component of a phage DNA injection site.
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PMID:Location and unusual membrane topology of the immunity protein of the Escherichia coli phage T4. 833 31

Protein import across both mitochondrial membranes is mediated by the cooperation of two distinct protein transport systems, one in the outer and the other in the inner membrane. Previously we described a 45 kDa yeast mitochondrial inner membrane protein (ISP45) that can be cross-linked to a partially translocated precursor protein (Scherer et al., 1992). We have now purified ISP45 to homogeneity and identified it as the product of the nuclear MPI1 gene. Identity of ISP45 with the MPI1 gene product was shown by microsequencing of three tryptic ISP45 peptides and by demonstrating that an antibody against an Mpi1p-beta-galactosidase fusion protein specifically recognizes ISP45. Antibodies monospecific for ISP45 inhibited protein import into right-side-out mitochondrial inner membrane vesicles, but not into intact mitochondria. On solubilizing mitochondria, ISP45 was rapidly converted to a 40 kDa proteolytic fragment unless mitochondria were first denatured with trichloroacetic acid. The combined genetic and biochemical evidence identifies ISP45/Mpi1p as a component of the protein import system of the yeast mitochondrial inner membrane.
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PMID:Protein import into yeast mitochondria: the inner membrane import site protein ISP45 is the MPI1 gene product. 834 45

The monoclonal antibody HPC-1 recognizes a protein antigen in the hippocampus, and its specific reactivity to the plasma membrane of the amacrine cell somas and the inner plexiform layer in rat retina has been reported. Sequencing the cDNA indicated in our previous study that the HPC-1 antigen was a membrane protein. By means of immunoblotting, an antiserum against the fusion protein of Escherichia coli beta-galactosidase and the HPC-1 antigen detected several proteins of about 35 kDa in the nervous tissues including retina, cerebral cortex, hippocampus, cerebellum and spinal cord, but no signal was obtained in the non-neuronal tissues. Immunofluorescent histochemistry of the various rat tissues revealed that the HPC-1 antigen was confined to the nervous system, including the matrices of the cerebral cortex and hippocampus, the molecular layer, membranes of granular cell somas and glomeruli in the cerebellum and gray matter of spinal cord. However, little staining was seen in the white matter of the central nervous tissues. Thus, the HPC-1 antigen was accumulated in the synapse-rich regions of neuronal cells. In situ hybridization revealed that the HPC-1 mRNA was present in most, if not all, neurons in the central and peripheral nervous systems except for the retina. In the retina, mRNA signals were detected in amacrine and ganglion cells in which HPC-1 immunoreactivity was absent in their soma, suggesting polarized localization of the HPC-1 mRNA on the ganglion cell axon terminal.
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PMID:Neuron specific expression of a membrane protein, HPC-1: tissue distribution, and cellular and subcellular localization of immunoreactivity and mRNA. 836 34


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