Biomedical subjects

Xiaofeng Lin

Publications and source records attributed to Xiaofeng Lin.

At least 19 recordsLinked to original sources

PubMed2007

Amphileptus aeschtae nov. spec. and Amphileptus eigneri nov. spec. (Ciliophora, Pleurostomatida), two new marine pleurostomatid ciliates from China.

The morphology and infraciliature of two pleurostomatid ciliates, Amphileptus aeschtae nov. spec. and Amphileptus eigneri nov. spec., collected from shrimp-culturing ponds of the Bohai Sea, China, were investigated using live observations and the protargol impregnation method. The new species A. aeschtae is identified by the presence of 200-300 macronuclear nodules and several contractile vacuoles along the ventral side of the cell. A. eigneri differs from its congeners, inter alia, by the marine habitat, the presence of many contractile vacuoles along the ventral margin and the number of somatic kineties on both sides. Loxophyllum ozakii Shigematsu, 1953 is transferred to Kentrophyllum.

Animals↗

PubMed2006

A new strategy to produce active human Src from bacteria for biochemical study of its regulation.

Enzymological studies of Src protein tyrosine kinase have been hindered by the lack of a suitable bacterial expression system. Poor expression of active Src appears to be due to toxicity associated with its kinase activity. To overcome this problem, we fused Src to a protein tyrosine phosphatase with an affinity tag and an appropriate thrombin cleavage site. Upon affinity purification of the fusion protein, Src was released by thrombin digestion and further purified by FPLC. This strategy has been used to produce several Src mutants that display catalytic and regulatory properties similar to those from eukaryotic expression systems. Characterization of the Src mutants confirmed that inactivation of Src by Csk through tail tyrosine phosphorylation required the Src SH3 domain.

Bacteria↗

PubMed2006

Conformational basis for SH2-Tyr(P)527 binding in Src inactivation.

Src protein-tyrosine kinase contains a myristoylation motif, a unique region, an Src homology (SH) 3 domain, an SH2 domain, a catalytic domain, and a C-terminal tail. The C-terminal tail contains a Tyr residue, Tyr527. Phosphorylation of Tyr527 triggers Src inactivation, caused by Tyr(P)527 binding to the SH2 domain. In this study, we demonstrated that a conformational contribution, not affinity, is the predominant force for the intramolecular SH2-Tyr(P)527 binding, and we characterized the structural basis for this conformational contribution. First, a phosphopeptide mimicking the C-terminal tail is an 80-fold weaker ligand than the optimal phosphopeptide, pYEEI, and similar to a phosphopeptide containing three Ala residues following Tyr(P) in binding to the Src SH2 domain. Second, the SH2-Tyr(P)527 binding is largely independent of the amino acid sequence surrounding Tyr(P)527, and only slightly decreased by an inactivating mutation in the SH2 domain. Furthermore, even the unphosphorylated C-terminal tail with the sequence of YEEI suppresses Src activity by binding to the SH2 domain. These experiments demonstrate that very weak affinity is sufficient for the SH2-Tyr(P)527 binding in Src inactivation. Third, the effective intramolecular SH2-Tyr(P)527 binding is attributed to a conformational contribution that requires residues Trp260 and Leu255. Although the SH3 domain is essential for Src inactivation by Tyr(P)527, it does not contribute to the SH2-Tyr(P)527 binding. These findings suggest a conformation-based Src inactivation model, which provides a unifying framework for understanding Src activation by a variety of mechanisms.

Amino Acid Motifs↗

PubMed2006

Synthesis and structure-activity relationships of linear and conformationally constrained peptide analogues of CIYKYY as Src tyrosine kinase inhibitors.

A series of peptide analogues of Ac-CIYKYY (1) were synthesized by functional group modifications in peptide side chains or by introducing conformational constraints, to improve the inhibitory potency against active Src kinase. Ac-CIYKF(4-NO2)Y (2, IC50 = 0.53 microM) and conformationally constrained peptide 31 (IC50 = 0.28 microM) exhibited 750- and 1400-fold higher inhibitory activities, respectively, versus that of 1 (IC50 = 400 microM). Compound 2 exhibited a partial competitive inhibition pattern against ATP.

Adenosine Triphosphate↗

PubMed2006

Structural basis for domain-domain communication in a protein tyrosine kinase, the C-terminal Src kinase.

The catalytic activity of protein tyrosine kinases is commonly regulated by domain-domain interactions. The C-terminal Src kinase (Csk) contains a catalytic domain and the regulatory SH3 and SH2 domains. Both the presence of the regulatory domains and binding of specific phosphotyrosine-containing proteins to the SH2 domain activate Csk. The structural basis for both modes of activation is investigated here. First, the SH3-SH2 linker is crucial for Csk activation. Mutagenic and kinetic studies demonstrate that this activation is mediated by a cation-pi interaction between Arg68 and Trp188. Second, Ala scanning and kinetic analyses on residues in the SH2-catalytic domain interface identify three functionally distinct types of residues in mediating the communication between the SH2 and the catalytic domains. Type I residues are important in mediating a ligand-triggered activation of Csk because their mutation severely reduces Csk activation by the SH2 domain ligand. Type II residues are involved in suppressing Csk activity, and their mutation activates Csk, but makes Csk less sensitive to activation by the SH2 ligand. Both type I and type II residues are likely involved in mediating SH2 ligand-triggered activation of Csk. Type III residues are those located in the SH2 domain whose mutation severely decreases Csk catalytic activity without affecting the SH2 ligand-triggered activation. These residues likely mediate SH2 activation of Csk regardless of SH2-ligand interaction. These studies lead us to propose a domain-domain communication model that provides functional insights into the topology of Csk family of protein tyrosine kinases.

Arginine↗

PubMed2006

[The change of transforming growth factor-beta1 in nonproliferation diabetic retinopathy].

PURPOSE: To evaluate the relationship between the level of transforming growth factor-beta1 (TGF-beta1) in serum of patients with nonproliferation diabetic retinopathy and the severity of this retinopathy, and to find out a new method for early intervention of diabetic retinopathy. METHOD: TGF-beta1 in serum was measured in the three groups as following: group DR containing the patients with nonproliferation diabetic retinopathy identified by funds fluorescein angiography, group DM consisting of diabetic without diabetic retinopathy, and group C containing healthy people, and analysed statistically. Then the patients with diabetic retinopathy were divided into three subgroups based on the phase of retinopathy: DR1, DR2, DR3, which results were also analysed statistically. RESULT: The level of TGF-beta1 in serum had no significant difference between the group DM and group C, and the level of the group DR was higher than group DM or the group C significantly. The level of the group DR1 was lower than the group DR2 DR3 significantly. CONCLUSION: In patients with nonproliferation diabetic retinopathy, the level of TGF-beta1, in serum is increased, and can reflect the severity of diabetic retinopathy. The level of TGF-beta1 in serum can also indicate the time of intervention to a certain extent.

Aged↗

PubMed2005

Characterization of the interactions between the active site of a protein tyrosine kinase and a divalent metal activator.

BACKGROUND: Protein tyrosine kinases are important enzymes for cell signalling and key targets for anticancer drug discovery. The catalytic mechanisms of protein tyrosine kinase-catalysed phosphorylation are not fully understood. Protein tyrosine kinase Csk requires two Mg2+ cations for activity: one (M1) binds to ATP, and the other (M2) acts as an essential activator. RESULTS: Experiments in this communication characterize the interaction between M2 and Csk. Csk activity is sensitive to pH in the range of 6 to 7. Kinetic characterization indicates that the sensitivity is not due to altered substrate binding, but caused by the sensitivity of M2 binding to pH. Several residues in the active site with potential of binding M2 are mutated and the effect on metal activation studied. An active mutant of Asn319 is generated, and this mutation does not alter the metal binding characteristics. Mutations of Glu236 or Asp332 abolish the kinase activity, precluding a positive or negative conclusion on their role in M2 coordination. Finally, the ability of divalent metal cations to activate Csk correlates to a combination of ionic radius and the coordination number. CONCLUSION: These studies demonstrate that M2 binding to Csk is sensitive to pH, which is mainly responsible for Csk activity change in the acidic arm of the pH response curve. They also demonstrate critical differences in the metal activator coordination sphere in protein tyrosine kinase Csk and a protein Ser/Thr kinase, the cAMP-dependent protein kinase. They shed light on the physical interactions between a protein tyrosine kinase and a divalent metal activator.

Binding Sites↗

PubMed2005

Probing the communication between the regulatory and catalytic domains of a protein tyrosine kinase, Csk.

Protein tyrosine kinases (PTKs) are important regulators of mammalian cell function and their own activities are tightly regulated. Underlying their tight regulation, all PTKs contain multiple regulatory domains in addition to a catalytic domain. C-terminal Src kinase (Csk) contains a catalytic domain and a regulatory region, consisting of an SH3 and an SH2 domain. In this study, we probed the communication between the regulatory and catalytic domains of Csk. First, kinetic characterization of SH3 and SH2 domain deletion mutants demonstrated that the SH3 and SH2 domains were crucial in maintaining the full activity of Csk, but were not directly involved in Csk recognition of its physiological substrate, Src. Second, highly conserved Trp188, corresponding to a key residue in domain-domain communication in other PTKs, was found to be important for maintaining the active structure of Csk by the presence of the regulatory region, but not required for Csk activation triggered by a phosphopeptide binding to the SH2 domain. Third, structural alignment indicated that the presence of the regulatory domains modulated the conformation of multiple substructures in the catalytic domain, some directly and others remotely. Mutagenic and kinetic studies supported this assignment. This report extended previous studies of Csk domain-domain communication, and provided a foundation for further detailed investigation of this communication.

Alanine↗

PubMed2005

[A case report of injecting gentamicin intraocularly by mistake being misdiagnosed as central retinal artery occlusion].

PURPOSE: To report a case receiving gentamicin injection intraocularly by mistake when subconjunctival injection and was misdiagnosed as central retinal artery occlusion. METHODS: After a complete examination, including ocular fundus examination, fundus fluorescein angiography (FFA) and indocyanine green angiography (ICGA), the correct diagnosis was confirmed. The patient received a surgery of vitrectomy. RESULTS: FFA revealed severe retinal vascular nonperfusion of the posterior pole. The final diagnosis was medicine toxic retinopathy from gentamicin. The visual acuity of the patient was counting figure/1 meter postoperationally. High intraocular pressure, scleral staphyloma and optic atrophy were detected during the follow-up. CONCLUSION: Injecting gentamicin intraocularly by accident usually resulted from carelessness. The massive doses of gentamicin might result in the severe retinal damage, which could be misdiagnosed as central retinal artery occlusion. Much attention should be paid to avoid its occurrence. The examination of FFA can help make correct diagnosis. Through the vitrectomy, though the damage could't be reversed thorougly, the surgery of vitrectomy could resume a little effective vision for the patient.

Administration, Topical↗

PubMed2004

Wide-range length metrology by dual-imaging-unit atomic force microscope based on porous alumina.

A new dual-imaging-unit atomic force microscope (DIU-AFM) was developed for wide-range length metrology. In the DIU-AFM, two AFM units were combined, one as a reference unit, and the other a test one. Their probes with Z piezo elements and tips were horizontally set in parallel at the same height to reduce errors due to geometric asymmetry. An XY scanner was attached to an XY block that was able to move in the X direction with a step of about 500 nm. A standard porous alumina film was employed as the reference sample. Both reference sample and test sample were installed at the center of the XY scanner on the same surface and were simultaneously imaged. The two images had the same lateral size, and thus the length of the test sample image could be accurately measured by counting the number of periodic features of the reference one. The XY block together with the XY scanner were next moved in the X direction for about 1.5 microm and a second pair of reference and test images were obtained by activating the scanner. In this way, a series of pairs of images were acquired and could be spliced into two wide-range reference and test images, respectively. Again, the two spliced images were of the same size and the length of test image was measured based on the reference one. This article presents a discussion about the structure and control of the DIU-AFM system. Some experiments were carried out on the system to demonstrate the method of length calculation and measurement. Experiments show a satisfactory result of wide-range length metrology based on the hexagonal features of the porous alumina with a periodic length of several tens of nanometers. Using this method the DIU-AFM is capable of realizing nanometer-order accuracy length metrology when covering a wide range from micron to several hundreds of microns, or even up to millimeter order.

Aluminum Oxide↗

PubMed2004

Nuclear translocation of EGF receptor regulated by Epstein-Barr virus encoded latent membrane protein 1.

Epstein-Barr virus (EBV) encoded latent membrane protein 1 (LMP1) is considered to be the major oncogenic protein of EBV encoded proteins, and also it has always been the core of the oncogenic mechanism of EBV. Traditional receptor theory demonstrates that cell surface receptors exert biological functions on the membrane, which neither enter into the nucleus nor directly affect the transcription of the target genes. But, advanced studies on nuclear translocation of the epidermal growth factor receptor (EGFR) family have greatly developed our knowledge of the biological function of cell surface receptors. In this study, we used Tet-on LMP1 HNE2 cell line as a cell model, which is a dual-stable LMP1 integrated NPC cell line and the expression of LMP1 in which could be regulated by Tet system. We found that LMP1 could regulate the nuclear translocation of EGFR in a dose-dependent manner from both quantitative and qualitative levels through the Western blot analysis and the immunofluorescent analysis with a laser scanning confocal microscope. We further demonstrated that the nuclear localization sequence of EGFR played some roles in the location of the protein within the nucleus under LMP1 regulation, and the nuclear accumulation of EGFR regulated by LMP1 was in a ligand-independent manner. These findings provide a novel view that the regulation of LMP1 on the nuclear translocation of EGFR is critical for the process of nasopharyngeal carcinoma.

Active Transport, Cell Nucleus↗

PubMed2004

The clinical analysis of endogenous endophthalmitis.

PURPOSE: To study the clinical characteristics, therapeutic efficacy and investigate prognostic factors of endogenous endophthalmitis. METHODS: Twenty-eight cases (28 eyes) of endogenous endophthalmitis were surveyed retrospectively. The clinical characteristics, primary infection foci, predisposing systemic disease, complications, pathogens examination, therapeutic options and efficacy were analysed. RESULTS: The endogenous endophthalmitis occurred more frequently in the right eye than in the left one. The respiratory tract was the most common primary foci. The positive rate of pathogens culture was higher in vitreous sample than that in other tissues. Cataract and retinal detachment were the common complications. The visual improvement and infection control were achieved in 13 eyes (46.43%). These 13 patients received treatment (3.77 +/- 2.49) days after onset of endophthalmitis being much earlier than that of others [(10.13 +/- 4.98) days, P = 0.002]. The prognosis was relevant to the type of the disease. The anterior segment inflammation type (anterior type) had better prognosis than posterior segment inflammation type (posterior type) and that of inflammation in both parts (mix type) (P < 0.05). There were no significant relation between the prognosis and the age, predisposing systemic disease, vitreous antibiotic injection and vitrectomy (P > 0.05). CONCLUSIONS: Endogenous endophthalmitis is a vital ocular emergency. Early diagnosis and effective treatment combination with systemic and local antibiotics are of significant value. The anterior type is prone to have better outcome than the others.

Adolescent↗

PubMed2004

Diagnostic ultrasound and pars plana vitrectomy in endophthalmitis.

PURPOSE: To compare the results by B-scan ultrasonography and findings in pars plana vitrectomy, and assess the diagnostic value of B-scan ultrasonography in endophthalmitis. METHODS: Thirty eyes of 30 subjects diagnosed as endophthalmitis were selected, who undergone preoperative B-scan ultrasonography. The result of pars plana vitrectomy was recorded. The above two results were compared. RESULTS: On the evaluation of vitreous and retinal states in the patients with endophthalmitis, the sensitivity of ultrasound was 90%-100%, and the specificity was 79%-100%. Poorer preoperative visual acuity was related with retinal detachment and retinal dissolution. The preoperative visual acuity in eyes with local vitreous opacity was better than with diffuse vitreous opacity. CONCLUSION: Comparison of the results of B-scan ultrasonography and the findings in pars plana vitrectomy showed B-scan ultrasonography is highly sensitive, specific, and is very helpful in the evaluation of endophthalmitis. B-scan ultrasonography can not only supply much information in the diagnosis of endophthalmitis but also inspect its trends and changes, which is helpful in the selection of treatment and planning the time of surgery.

Adolescent↗

PubMed2004

Clinic analysis of Behçet disease.

PURPOSE: To analyze the clinic manifestation and prognosis of Behçet disease. METHOD: Twenty patients requiring inpatient treatment with Behçet disease were retrospectively analyzed. RESULTS: The morbidity of Behçet disease is 5.5/100 000. In the systemic damage, stomatocace and skin lesion are 95%, eye lesion and genital ulcer 50%, joint lesion 45%, gastrointestinal lesion 35%, Uveitis is the major disease in eye lesion, and followed in order by retinal vasculitis and obstruction of retinal artery. Attack age average 30.3 years old. Diagnosis age average 34.8 years old. The patients stay in hospital for 41 days on the average. Cure rate is 55%, improvement rate 40%, blinding rate of eye lesion is 36%. CONCLUSIONS: Behçet disease is a multisystem lesion disease. Stomatocace and skin lesion is the major lesion, the next in common occurrence are eye and genital lesions. Repeated attack of uveitis, complicated cataract and secondary glaucoma are the major causes of blindness.

Adolescent↗

PubMed2003

Determination of the substrate-docking site of protein tyrosine kinase C-terminal Src kinase.

Protein tyrosine kinases (PTK) are key enzymes of mammalian signal transduction. For the fidelity of signal transduction, each PTK phosphorylates only one or a few proteins on specific Tyr residues. Substrate specificity is thought to be mediated by PTK-substrate docking interactions and recognition of the phosphorylation site sequence by the kinase active site. However, a substrate-docking site has not been determined on any PTK. C-terminal Src kinase (Csk) is a PTK that specifically phosphorylates Src family kinases on a C-terminal Tyr. In this study, by sequence alignment and site-specific mutagenesis, we located a substrate-docking site on Csk. Mutations in the docking site disabled Csk to phosphorylate, regulate, and complex with Src but only moderately affected its general kinase activity. A peptide mimicking the docking site potently inhibited (IC50 = 21 microM) Csk phosphorylation of Src but only moderately inhibited (IC50 = 422 microM) its general kinase activity. Determination of the substrate-docking site provides the structural basis of substrate specificity in Csk and a model for understanding substrate specificity in other PTKs.

Alanine↗

PubMed2003

Functions of the activation loop in Csk protein-tyrosine kinase.

Autophosphorylation in the activation loop is a common mechanism regulating the activities of protein-tyrosine kinases (PTKs). PTKs in the Csk family, Csk and Chk, are rare exceptions for lacking Tyr residues in this loop. We probed the function of this loop in Csk by extensive site-specific mutagenesis and kinetic studies using physiological and artificial substrates. These studies led to several surprising conclusions. First, specific residues in Csk activation loop had little discernable functions in phosphorylation of its physiological substrate Src, as Ala scanning and loop replacement mutations decreased Csk activity toward Src less than 40%. Second, some activation loop mutants, such as a single residue deletion or replacing all residues with Gly, exhibited 1-2% of wild type (wt) activity toward artificial substrates, but significantly higher activity toward Src. Third, introduction of a thrombin cleavage site to the activation loop also resulted in loss of 98% of wt activity for poly(E4Y) and loss of 95% of wt activity toward Src, but digestion with thrombin to cut the activation loop, resulted in full recovery of wt activity toward both substrates. This suggested that the catalytic machinery is fully functional without the activation loop, implying an inhibitory role by the activation loop as a regulatory structure. Fourth, Arg313, although universally conserved in protein kinases, and essential for the activity of other PTKs so far tested, is not important for Csk activity. These findings provide new perspectives for understanding autophosphorylation as a regulatory mechanism and imply key differences in Csk recognition of artificial and physiological substrates.

Amino Acid Sequence↗

PubMed2003

[Sympathetic ophthalmia caused by ocular penetration with endophthalmitis].

PURPOSE: To summarize the clinical features, diagnosis and treatment of sympathetic ophthalmia caused by ocular penetration with endophthalmitis. METHODS: Retrospective analysis was done on clinical data of 3 cases of sympathetic ophthalmia with ocular penetration and endophthalmitis. RESULTS: 5,253 cases of ocular penetration and fracture were hospitalized from 1993 to 2002, while 87 cases of sympathetic ophthalmia were found at the same period of time, with the ratio of 1.65%. 3 cases had history of ocular penetration with endophthalmitis. Fluorescein angiography indicated that these 3 cases had developed sympathetic ophthalmia. Microscopic examination showed that 1 case had typical histological changes of sympathetic ophthalmia. CONCLUSION: Sympathetic ophthalmia caused by ocular penetration with endophthalmitis is infrequent, but this situation should not be neglect.

Adult↗

PubMed2003

[Autocorneoscleral reconstruction for the treatment of recurrent pterygium].

PURPOSE: To evaluate the therapeutic effects of autocorneoscleral reconstruction for the treatment of recurrent pterygium. METHODS: Autocorneoscleral reconstruction were performed on 22 cases (22 eyes) with recurrent pterygium. RESULTS: Tweuty-two cases have stable corneal epithelial healing and transparent graft, no recurred pterygium was found after the operation. CONCLUSIONS: Autocorneoscleral reconstruction is effective and safe for the treatment of recurrent pterygium.

Adult↗