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ABSTRACT: The α(7) acetylcholine receptor (AChR) mediates pre- and postsynaptic neurotransmission in the central nervous system and is a potential therapeutic target in neurodegenerative, neuropsychiatric and inflammatory disorders. We determined the crystal structure of the extracellular domain of a receptor chimera constructed from the human α(7) AChR and Lymnaea stagnalis acetylcholine binding protein (AChBP), which shares 64% sequence identity and 71% similarity with native α(7). We also determined the structure with bound epibatidine, a potent AChR agonist. Comparison of the structures revealed molecular rearrangements and interactions that mediate agonist recognition and early steps in signal transduction in α(7) AChRs. The structures further revealed a ring of negative charge within the central vestibule, poised to contribute to cation selectivity. Structure-guided mutational studies disclosed distinctive contributions to agonist recognition and signal transduction in α(7) AChRs. The structures provide a realistic template for structure-aided drug design and for defining structure-function relationships of α(7) AChRs.
Nature Neuroscience 09/2011; 14(10):1253-9. · 15.53 Impact Factor
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Shu-Xing Li,
Yong-Ping Tong,
Xiao-Cong Xie,
Qi-Hai Wang,
Hui-Na Zhou,
Yi Han,
Zhan-Yu Zhang,
Wei Gao,
Sheng-Guang Li,
Xuejun C Zhang,
Ru-Chang Bi
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ABSTRACT: Phosphoribosylaminoimidazole carboxylase/phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS) is an important bifunctional enzyme in de novo purine biosynthesis in vertebrate with both 5-aminoimidazole ribonucleotide carboxylase (AIRc) and 4-(N-succinylcarboxamide)-5-aminoimidazole ribonucleotide synthetase (SAICARs) activities. It becomes an attractive target for rational anticancer drug design, since rapidly dividing cancer cells rely heavily on the purine de novo pathway for synthesis of adenine and guanine, whereas normal cells favor the salvage pathway. Here, we report the crystal structure of human PAICS, the first in the entire PAICS family, at 2.8 A resolution. It revealed that eight PAICS subunits, each composed of distinct AIRc and SAICARs domains, assemble a compact homo-octamer with an octameric-carboxylase core and four symmetric periphery dimers formed by synthetase domains. Based on structural comparison and functional complementation analyses, the active sites of SAICARs and AIRc were identified, including a putative substrate CO(2)-binding site. Furthermore, four symmetry-related, separate tunnel systems in the PAICS octamer were found that connect the active sites of AIRc and SAICARs. This study illustrated the octameric nature of the bifunctional enzyme. Each carboxylase active site is formed by structural elements from three AIRc domains, demonstrating that the octamer structure is essential for the carboxylation activity. Furthermore, the existence of the tunnel system implies a mechanism of intermediate channeling and suggests that the quaternary structure arrangement is crucial for effectively executing the sequential reactions. In addition, this study provides essential structural information for designing PAICS-specific inhibitors for use in cancer chemotherapy.
Journal of Molecular Biology 04/2007; 366(5):1603-14. · 4.00 Impact Factor
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ABSTRACT: Septin 1 is a member of an evolutionarily conserved family of GTP-binding and filament-forming proteins named septins, which function in diverse processes including cytokinasis, vesicle trafficking, apoptosis, remodelling of the cytoskeleton, infection, neurodegeneration and neoplasia. Human septin 1 has been expressed and purified, but suffers from severe aggregation. Studies have shown that septin 1 with site-directed mutations of five serine residues (Ser19, Ser206, Ser307, Ser312 and Ser315) has a much lower degree of aggregation and better structural homogeneity and that the mutations cause only slight perturbations in the secondary structure of septin 1. This septin 1 mutant was crystallized and diffraction data were collected to 2.5 A resolution. The space group is P422, with unit-cell parameters a = b = 106.028, c = 137.852 A.
Acta Crystallographica Section F Structural Biology and Crystallization Communications 03/2006; 62(Pt 2):128-32. · 0.51 Impact Factor
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ABSTRACT: Macromolecular crystallization remains a bottleneck in structure determination by X-ray diffraction. Based on the data reflecting success rates of crystallization conditions in different screens and the information derived from the BMCD and other related studies, a simplified screen has been designed to increase the success rate of traditional screening and to save samples, time and cost. The screen has been tested with six protein samples which had been crystallized before and its comparison with Crystal Screen (Hampton Research) was also performed with lysozyme crystallization. The experimental results show that for obtaining crystal leads, the success rate of the simplified screen is reasonably higher. In addition, it has been successful in crystallizing two new proteins from snake venom using the simplified screen that had failed with Crystal Screen. These results indicate that the simplified screen, which assembles and optimizes the efficient crystallization conditions from distinct screens, extends the region of crystallization and improves the success rate of screening. Based on information of newly published efficient crystallization conditions, the simplified screen could be developed and optimized continuously in the future.
Acta Crystallographica Section D Biological Crystallography 07/2005; 61(Pt 6):776-9. · 12.62 Impact Factor
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ABSTRACT: The crystal structure of the bacterioferritin from Azotobacter vinelandii has been determined at 2.6 A resolution. Both the low occupancy of one iron ion in the dinuclear iron center and the deviation of its adjacent residue His130 from the center suggest migration of the iron ion from the dinuclear iron site to the inner nucleation site. The concerted movement of His130 and Glu47 may admit a dynamic gating mechanism for shift of the oxidized iron ion. Ba2+ binding to the fourfold channel implicates that the channel bears Fe2+ conductivity and selectivity to provide a route for iron access to the inner cavity during core formation.
FEBS Letters 09/2004; 573(1-3):93-8. · 3.54 Impact Factor
