Biomedical subjects

Guang-Yao Li

Publications and source records attributed to Guang-Yao Li.

5 recordsLinked to original sources

PubMed2006

Stored Ca2+ depletion-induced oligomerization of stromal interaction molecule 1 (STIM1) via the EF-SAM region: An initiation mechanism for capacitive Ca2+ entry.

Stromal interaction molecule 1 (STIM1) has recently been identified as a key player in store-operated Ca2+ entry. Endoplasmic reticulum (ER) luminal Ca2+ depletion results in STIM1 redistribution from ER membrane homogeneity to distinctly localized aggregates near the plasma membrane; these changes precede and are linked to cytoplasmic Ca2+ influx via Ca2+ release-activated channels (CRACs). The molecular mechanisms initiating ER STIM1 redistribution and plasma membrane CRAC activity are not well understood. We recombinantly expressed the Ca2+-sensing region of STIM1 consisting of the EF-hand together with the sterile alpha-motif (SAM) domain (EF-SAM) to investigate its Ca2+-related conformational and biochemical features. We demonstrate that Ca2+-loaded EF-SAM (holo) contains high alpha-helicity, whereas EF-SAM in the absence of Ca2+ (apo) is much less compact. Accordingly, the melting temperature (Tm) of the holoform is approximately 25 degrees C higher than apoform; heat and urea-derived thermodynamic parameters indicate a Ca2+-induced stabilization of 3.2 kcal mol(-1). We show that holoEF-SAM exists as a monomer, whereas apoEF-SAM readily forms a dimer and/or oligomer, and that oligomer to monomer transitions and vice versa are at least in part mediated by changes in surface hydrophobicity. Additionally, we find that the Ca2+ binding affinity of EF-SAM is relatively low with an apparent dissociation constant (Kd) of approximately 0.2-0.6 mM and a binding stoichiometry of 1. Our results suggest that EF-SAM actively participates in and is the likely the molecular trigger initiating STIM1 punctae formation via large conformational changes. The low Ca2+ affinity of EF-SAM is reconciled with the confirmed role of STIM1 as an ER Ca2+ sensor.

Calcium↗

PubMed2005

Characterization of dual substrate binding sites in the homodimeric structure of Escherichia coli mRNA interferase MazF.

MazF and MazE constitute a so-called addiction module that is critical for bacterial growth arrest and eventual cell death in response to stress. The MazF toxin was recently shown to possess mRNA interferase (MIase) activity, and acts as a protein synthesis inhibitor by cleaving cellular mRNA. As a cognate regulator, the short-lived antitoxin, MazE, inhibits MazF MIase activity and hence maintains the delicate homeostasis between these two components. In the present study, we have shown that the MazF homodimer contains two symmetric binding sites, each of which is capable of interacting with a MazE C-terminal peptide, MazEp(54-77). The slow exchange phenomenon between free and peptide-bound MazF on the NMR timescale indicates relatively high affinities for MazEp(54-77) at both sites (Kd,K'd < 10(-7) M). However, the observed sequential binding behavior suggests a negative cooperativity between the two sites (Kd < K'd). A 13 base single-stranded DNA, employed as an uncleavable RNA substrate analog, can also bind to both sites on the MazF homodimer with moderate affinity (Kd approximately 10(-5) -10(-6) M). Chemical shift perturbation data deduced from NMR experiments indicates that the two binding sites for the MazEp peptide coincided with those for the single-stranded DNA competitive inhibitor. These dual substrate-binding sites are located on the concave interface of the MazF homodimer, consisting of a highly basic region underneath the S1-S2 loop and two hydrophobic regions containing the H1 helix of one subunit and the S3-S4 loop of the opposing subunit. We show that the MazF homodimer is a bidentate endoribonuclease equipped with two identical binding sites for mRNA processing and that a single MazE molecule occupying one of the binding sites can affect the conformation of both sites, hence efficiently hindering the activity of MazF.

Amino Acid Sequence↗

PubMed2004

[Three-dimensional reconstruction on facial soft tissue using three-dimensional grating projection technique].

PURPOSE: The purpose of this study is to establish a method to reconstruct the facial soft tissue three-dimensionally. METHODS: By ATOS three-dimensional opticalmetry, which used in industry, 3D data on facial profile of a patient with mandibular hyperplasia was achieved quickly. RESULTS: Three-dimensional data of facial profile was accurate and the images were reconstructed with verisimilitude. CONCLUSIONS: Traditional device of grating projection was modified by using two CCD cameras to obtain grating images.3D data on facial profile were achieved quickly and accurately.

Adult↗

PubMed2003

A new triterpenoid from Entodon okamurae Broth.

One new triterpenoid, entokamurol (1), was isolated from Entodon okamurae Broth, together with other nine compounds, namely dryocrassol (2), chrysophamol (3), physcion (4), 10-nonacosamnol (5), n-hexadecanol (6), phthalic acid isodibutyl ester (7), curcumol (8), beta-sitosterol (9) and daucosterol (10). Their structures were elucidated on the basis of extensive NMR (DEPT, DQF-COSY, HMQC, HMBC and NOESY), IR and MS studies. All the compounds were isolated and identified from the genus of Entodon for the first time, and it is also the first report of a guaiane-type sesquiterpenoid and compounds with anthraquinone skeleton in mosses.

Bryophyta↗

PubMed2002

A cytotoxic diterpenoid and antifungal phenolic compounds from Frullania muscicola Steph.

A novel ent-labdane type diterpenoid, muscicolone (1), as well as two bibenzyls (2, 3) and four flavonoids (4-7) were isolated from the liverwort Frullania muscicola Steph. Their structures were established by analysis of the spectral data of IR, UV, ID-, 2D-NMR, and ORD. The stereostructure of 1 was confirmed by X-ray crystallographic analysis. Bioassay experiments showed that compound 3 and 4 have potent inhibitory effects against some fungi while 1 showed cytotoxic effects to some human tumor cells.

Antifungal Agents↗