Biomedical subjects

X Qian

Publications and source records attributed to X Qian.

175 records · Page 10Linked to original sources

PubMed1992

Two-dimensional NMR studies of the zinc finger motif: solution structures and dynamics of mutant ZFY domains containing aromatic substitutions in the hydrophobic core.

Solution structures of mutant Zn fingers containing aromatic substitutions in the hydrophobic core are determined by 2D-NMR spectroscopy and distance-geometry/simulated annealing (DG/SA). The wild-type domain (designated ZFY-6) is derived from the human male-associated protein ZFY and represents a sequence motif (Cys-X2-Cys-X-Ar-X7-Leu-X2-His-X4-His) that differs from the consensus (Cys-X2,4-Cys-X3-Phe-X5-Leu-X2-His-X3-His) in the location ("aromatic swap") and diversity (Ar = tyrosine, phenylalanine, or histidine) of the central aromatic residue (underlined). In a given ZFY domain the choice of a particular aromatic residue is invariant among vertebrates, suggesting that alternative "swapped" aromatic residues are functionally inequivalent. 2D-NMR studies of analogues containing tyrosine, phenylalanine, or histidine at the swapped site yield the following results. (i) The three DG/SA structures each retain the beta beta alpha motif and exhibit similar staggered-horizontal packing between the variant aromatic residue and the proximal histidine in the hydrophobic core. (ii) The structures and stabilities of the tyrosine and phenylalanine analogues are essentially identical, differing only by local exposure of polar (Tyr p-OH) or nonpolar (Phe p-H) surfaces. (iii) The dynamic stability of the histidine analogue is reduced as indicated by more rapid protein-deuterium exchange of hydrogen bonds related to secondary structure and amide-sulfur coordination (slowly exchanging amide resonances in D2O) and by more extensive averaging of main-chain dihedral angles (3J alpha NH coupling constants). An aspartic acid in the putative DNA recognition surface, whose configuration is well-defined as a possible helix N-cap in the tyrosine and phenylalanine analogues, exhibits multiple weak main-chain contacts in the NOESY spectrum of the histidine analogue; such NOEs are geometrically inconsistent and so provide complementary evidence for structural fluctuations. (iv) Because the three DG ensembles have similar apparent precision, the finding of reduced dynamic stability in the histidine analogue emphasizes the importance of experiments that directly probe fluctuations at several time scales. Our results provide insight into the design of biological metal-binding sites and the relationship of protein sequence to structure and dynamics.

Amino Acid Sequence↗

PubMed1992

Hepatocyte nuclear factor 3 beta contains two transcriptional activation domains, one of which is novel and conserved with the Drosophila fork head protein.

The hepatocyte nuclear factor 3 (HNF-3) gene family is composed of three proteins (alpha, beta, and gamma) that are transcription factors involved in the coordinate expression of several liver genes. All three proteins share strong homology in their DNA binding domains (region I) and are able to recognize the same DNA sequence. They also possess two similar stretches of amino acids at the carboxyl terminus (regions II and III) and a fourth segment of homology at the amino terminus (region IV). Furthermore, the HNF-3 proteins demonstrate homology with the Drosophila homeotic gene fork head in regions I, II, and III, suggesting that HNF-3 may be its mammalian homolog. In order to define HNF-3 beta protein domains involved in transcriptional activation, we have used a reporter gene, whose transcription is dependent on HNF-3 binding, for hepatoma cell cotransfection assays with expression vectors that produced different truncated HNF-3 beta proteins. A position-independent activation domain which contained conserved regions II and III was identified at the carboxyl terminus of the HNF-3 beta protein (amino acids 361 to 458). Moreover, site-directed mutations that altered the sequences within regions II and III demonstrated their importance to transactivation. The region II-III domain does not possess amino acid sequences in common with other transcription factors and may define a novel activation motif. HNF-3 beta amino-terminal sequences defined by conserved region IV also contributed to transactivation, but region IV activity required the participation of the region II-III domain. Region IV is abundant in serine amino acids and contains two putative casein kinase I phosphorylation sites, a feature similar to protein motifs described for the transcription factors Pit-1/GHF-1 and HNF-1.

Amino Acid Sequence↗

PubMed1990

[Treatment of hereditary angioedema].

Hereditary angioedema is a rare familial disease caused by the defect of complement C1esterase inhibitor (C1-INH). It is characterized by recurrent acute edema of the extremities, the face, the respiratory tract and the gastrointestinal tract. Acute laryngeal edema usually produces laryngeal obstruction. Two cases have been treated since 1986, one of them had been admitted for forty-five times because of recurrent acute laryngeal edema. Investigations showed two families with a high incidence of this disease. Laboratory examination showed a remarkable decrease of C1-INH and C4. Tracheotomy is indicated in patients with laryngeal edema. Great success was achieved in two patients treated with danazol.

Angioedema↗

PubMed1990

[Pathologic morphology of the indented tongue].

This paper use the methods of light microscope, electronmicroscope to observe the appearance of pathology and morphology of the convex and concave parts of the indented tongue edge, and examine the histology of normal tongue edge as a contrast. The authors consider that the main pathological changes of the indented tongue are: Thinning of the epithelial layer; change of rough endoplastic retica; reducing in tonofilaments; edema of cells and tissues, and decreasing in elastic fibers and collagenic fibers, etc.

Adult↗

PubMed1988