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81.
Mathias Grote Yevhen Polyhach Gunnar Jeschke Heinz-J��rgen Steinhoff Erwin Schneider Enrica Bordignon 《The Journal of biological chemistry》2009,284(26):17521-17526
ABC transporters are ubiquitous membrane proteins that translocate solutes across biological membranes at the expense of ATP. In prokaryotic ABC importers, the extracytoplasmic anchoring of the substrate-binding protein (receptor) is emerging as a key determinant for the structural rearrangements in the cytoplasmically exposed ATP-binding cassette domains and in the transmembrane gates during the nucleotide cycle. Here the molecular mechanism of such signaling events was addressed by electron paramagnetic resonance spectroscopy of spin-labeled ATP-binding cassette maltose transporter variants (MalFGK2-E). A series of doubly spin-labeled mutants in the MalF-P2 domain involving positions 92, 205, 239, 252, and 273 and one triple mutant labeled at positions 205/252 in P2 and 83 in the Q-loop of MalK were assayed. The EPR data revealed that the substrate-binding protein MalE is bound to the transporter throughout the transport cycle. Concomitantly with the three conformations of the ATP-binding cassette MalK2, three functionally relevant conformations are found also in the periplasmic MalF-P2 loop, strictly dependent on cytoplasmic nucleotide binding and periplasmic docking of liganded MalE to MalFG. The reciprocal communication across the membrane unveiled here gives first insights into the stimulatory effect of MalE on the ATPase activity, and it is suggested to be an important mechanistic feature of receptor-coupled ABC transporters. 相似文献
82.
Mark H. Doolittle Saskia B. Neher Osnat Ben-Zeev Jo Ling-liao Ciara M. Gallagher Maryam Hosseini Fen Yin Howard Wong Peter Walter Mikl��s P��terfy 《The Journal of biological chemistry》2009,284(48):33623-33633
Lipase maturation factor 1 (LMF1) is predicted to be a polytopic protein localized to the endoplasmic reticulum (ER) membrane. It functions in the post-translational attainment of enzyme activity for both lipoprotein lipase and hepatic lipase. By using transmembrane prediction methods in mouse and human orthologs, models of LMF1 topology were constructed and tested experimentally. Employing a tagging strategy that used insertion of ectopic glycan attachment sites and terminal fusions of green fluorescent protein, we established a five-transmembrane model, thus dividing LMF1 into six domains. Three domains were found to face the cytoplasm (the amino-terminal domain and loops B and D), and the other half was oriented to the ER lumen (loops A and C and the carboxyl-terminal domain). This representative model shows the arrangement of an evolutionarily conserved domain within LMF1 (DUF1222) that is essential to lipase maturation. DUF1222 comprises four of the six domains, with the two largest ones facing the ER lumen. We showed for the first time, using several naturally occurring variants featuring DUF1222 truncations, that Lmf1 interacts physically with lipoprotein lipase and hepatic lipase and localizes the lipase interaction site to loop C within DUF1222. We discuss the implication of our results with regard to lipase maturation and DUF1222 domain structure. 相似文献
83.
Mihály L. Kecskés Michael T. Rose Erwin Michel Benôit Lauby Malala Rakotondrainibe Andrea Casteriano Attila Palágyi Anaëlle Moutouvirin Sébastien Elter Romain Guillas Ganisan Krishnen Ivan R. Kennedy 《Engineering in Life Science》2009,9(6):431-436
Rapid, specific techniques are essential to monitor the quality of inoculant plant growth‐promoting strains at all stages of manufacture from starter culture to the final product in its carrier medium. In this study, colony immunoblotting was evaluated for the specific detection and enumeration of Citrobacter freundii, one component of a Vietnamese commercial inoculant plant growth‐promoting product used to improve the yield and nutrient efficiency of paddy rice. For quality control of either sterilised or unsterilised carrier media in commercial products colony immunoblotting proved to be a promising tool. Furthermore, it was possible using this technique to measure the survival of this strain in soil and the rhizosphere. 相似文献
84.
This review discusses the various aspects of the bio-geochemistry of germanium, and of its technological, economical and environmental
importance. Despite the relatively low annual production and consumption of this semi-metal (ca. 80 metric tons/a) there are
important technological applications of this element in the semiconductor, infrared optics and fibre optics/telecommunication
industries. A small, but not insignificant fraction of this element is used for the production of pharmaceuticals and nutritional
supplements, although its actual merits have not been fully demonstrated yet, while they are opposed to chronic toxicity of
the element when being administrated at relatively high doses for an extended period of time. Neither the exact mechanism
of action in the case of cancer treatment or the treatment of infectious diseases is known, nor the reason for the toxicity
of inorganic species of this element. In plants, Ge can partially substitute for B in the case of boron deficiency, although
deficiency symptoms are still seen with a lag period of ca. one to three weeks. In biogeochemical respect, germanium and silicon
react very similar, as if Ge were a very heavy isotope of Si. Their molar ratio is typically in the order of 0.6 × 10−6, with significant deviations only where germanium is complexed and transported, e.g., by humic-rich waters. Germanium is
a very conservative element in biogeochemical terms: It hardly shows involvement in any biogeochemical reaction cycles and
is mainly present in the form of complexes or hydroxo-compounds of the tetravalent germanium. The only naturally occurring
organogermanium compounds are mono- and dimethylgermanium which are believed to be formed by microbiological activity in continental
zones containing Ge-rich minerals, and then are leached into rivers, and finally into the open sea. It becomes evident that,
although very sophisticated technological uses of germanium exist, a better understanding of its biogeochemical importance,
cycling and reactivity must still be developed. 相似文献
85.
86.
87.
Spencer E. Taylor Erwin Buncel Albert R. Norris 《Journal of inorganic biochemistry》1981,15(2):131-141
Proton nmr spectroscopic evidence is presented for methylmercury(II) binding to the deprotonated amino groups in adenosine, 9-methyladenine, guanosine, 1-methylguanosine, and cytidine under basic conditions. Except for the guanosine case, 1H nmr spectra of the products from aqueous or ethanolic 1:1 mixtures of substrate and MeHgOH are consistent with methylmercuration of the deprotonated amino groups. Guanosine undergoes initial binding of MeHg to N1, and a second equivalent of MeHgOH is necessary to effect amino binding. The nmr spectra of the complexed adenine derivatives suggest that different geometrical isomers exist in (CD3)2SO solution, reflecting the partial double bond character of the C6N bond in these systems. Using a correlation relating the magnitude of the 199Hg-1H coupling constant (J) for MeHg-ligand complexes with the ligand pKa (J = ?3.88 pKa + 248.5, extending over 13 pK units, based on a variety of N and O donor ligands), estimates (± 0.3 pK unit) of the pKas of the amino groups of the above substrates have been made. In this way, pKa values of 15.5 (cytidine), 17.0 (adenosine and 9-methyladenine), 15.1 (guanosine), and 14.9 (1-methylguanosine) are obtained. In the cases where comparisons with literature pKa data can be made, good agreement is found. 相似文献
88.
89.
90.
Christine Rauch Michael Trieb Fajar R. Wibowo Bernd Wellenzohn Erwin Mayer Klaus R. Liedl 《Journal of biomolecular structure & dynamics》2013,31(6):695-706
Abstract CpG methylation determines a variety of biological functions of DNA. The methylation signal is interpreted by proteins containing a methyl-CpG binding domain (MBDs). Based on the NMR structure of MBD1 complexed with methylated DNA we analysed the recognition mode by means of molecular dynamics simulations. As the protein is monomeric and recognizes a symmetrically methylated CpG step, the recognition mode is an asymmetric one. We find that the two methyl groups do not contribute equally to the binding energy. One methyl group is associated with the major part of the binding energy and the other one nearly does not contribute at all. The contribution of the two cytosine methyl groups to binding energy is calculated to be ?3.6 kcal/mol. This implies a contribution of greater than two orders of magnitude to the binding constant. The conserved amino acid Asp32 is known to be essential for DNA binding by MBD1, but so far no direct contact with DNA has been observed. We detected a direct DNA base contact to Asp32. This could be the main reason for the importance of this amino acid. MBD contacts DNA exclusively in the major groove, the minor groove is reserved for histone contacts. We found a deformation of the minor groove shape due to complexation by MBD1, which indicates an information transfer between the major and the minor groove. 相似文献