The DC gate in Channelrhodopsin-2: crucial hydrogen bonding interaction between C128 and D156

The light-gated cation channel Channelrhodopsin-2 (ChR2), a retinylidene protein found in the eye-spot of Chlamydomonas reinhardtii, became an optogenetic tool to trigger neurophysiological responses by light and, thus, revolutionized spatio-temporal studies of such processes. The reaction mechanism still remains elusive but recent vibrational spectroscopic experiments started to resolve details of the associated structural changes during the photocycle. Large alterations in the polypeptide backbone were observed by FT-IR spectroscopy that precede and succeed the opening and closing of the channel, respectively. However, the molecular switch that controls gating is still unknown. Here, we present difference spectra of the D156E mutant of ChR2 and assign the observed vibrational bands to crucial hydrogen bonding changes of this residue in various intermediate states of the photoreaction. By comparison with spectra of wild-type ChR2 and the C128T mutant and correlation to electrophysiological studies, we propose the DC gate as a crucial hydrogen-bonding interaction between D156 and C128 which may represent the valve of the channel.

Lack of association between ACE ID polymorphism and colorectal cancer in Romanian patients

BACKGROUND

The insertion/deletion polymorphism of the angiotensin I-converting enzyme (ACE) gene has recently been linked to the pathogenesis of human cancers. The goal of this study was to analyze the possible association between ACE gene I/D polymorphism and colorectal cancer in Romanian patients.

METHODS

Blood samples were obtained, after informed consent, from individuals with colorectal cancer (n=108, M:W = 64:44), and healthy persons (n=150, M:W = 84:66). Genomic DNA was extracted from peripheral blood leucocytes using commercial kits and the insertion (I) / deletion (D) polymorphism was assessed by PCR. Statistical analysis was done using the chi2 test. We determined the odds ratio using the genotype II as risk factor. A p value < 0.05 was considered statistically significant.

RESULTS

The distribution of ACE II: ID: DD genotypes was 23.1%: 46.3%: 30.6% in patients and respectively 20%: 48.7%: 31.3% in controls. The distribution of genotype (chi2 0.37, p = 0.54) and alleles (chi2 0.19, p = 0.65) did not differ significantly between cancer patients and control.

CONCLUSIONS

Study results do not demonstrate an association between ACE ID polymorphism and colorectal cancer in our patients.

Conformational changes of channelrhodopsin-2

Channelrhodopsin-2 (ChR2) is a member of the new class of light-gated ion channels which serve as phototaxis receptors in the green alga Chlamydomonas reinhardtii. The protein is employed in optogenetics where neural circuits are optically stimulated under high spatiotemporal control. Despite its rapidly growing use in physiological experiments, the reaction mechanism of ChR2 is poorly understood. Here, we applied vibrational spectroscopy to trace structural changes of ChR2 after light-excitation of the retinal chromophore. FT-IR difference spectra of the various photocycle intermediates revealed that stages of the photoreaction preceding (P(1) state) and succeeding (P(4)) the conductive state of the channel (P(3)) are associated with large conformational changes of the protein backbone as indicate by strong differences in the amide I bands. Critical hydrogen-bonding changes of protonated carboxylic amino acid side chains (D156, E90) were detected and discussed with regard to the functional mechanism. We used the C128T mutant where the lifetime of P(3) is prolonged and applied FT-IR and resonance Raman spectroscopy to study the conductive P(3) state of ChR2. Finally, a mechanistic model is proposed that links the observed structural changes of ChR2 to the changes in the channel's conductance.

Laser-induced magnetization dynamics of lanthanide-doped permalloy thin films

We investigate the effect of Ho, Dy, Tb, and Gd impurities on the femtosecond laser-induced magnetization dynamics of thin Permalloy films using the time-resolved magneto-optical Kerr effect. Varying the amount of Ho, Dy, Tb content from 0% to 8%, we observe a gradual change of the characteristic demagnetization time constant from approximately 60 to approximately 150 fs. In contrast, Gd concentrations up to 15% do not influence the time scale of the initial photoinduced magnetization loss. We propose a demagnetization mechanism that relies on strong magnetic inertia of the rare-earth dopant which stabilizes the ferrimagnetic ordering and thereby delays the demagnetization.

Molecular analysis of mutations for the adenomatous polyposis coli (APC) gene in Romanian patients with colorectal cancer

Mutations in adenomatous polyposis coli (APC) gene have not been previously characterized among Romanian patients with colorectal cancer (CRC). We initiate this study to detect the mutations in APC gene in blood and tumor samples collected from 16 patients (10 men and 6 women) and blood samples from 21 first and second degree relatives of the patients. For this the presence of mutations in exons 6, 7, 12, 13, 14 as well as in regions B, L and W of exon 15 was investigated using PCR multiplex. In the same time, we have searched for 5 bp deletions at codon 1061 of APC gene by PAGE and SSCP methods. These methods allowed us to evidence identification of the presence of mutations in samples from 7 individuals. In one patient, was detected a deletion of exon 13th of APC gene both in DNA extracted from blood and tumor samples. Multiple deletions (e.g. in exon 6, 12, and in 15L and 15W regions) in DNA extracted from the tumor sample were detected, but not in DNA probe obtained from blood cells. We can speculate that these mutations are an example of genomic instability accompanying the malignancy. Till now, no mutation affecting 1061 codon of APC gene was identified in the patients investigated in our study.

[The ostomy support team. A reality for ostomates]

Stoma is a Greek word meaning mouth or opening. There are many types of surgical stomas and they may be raised on many areas of the abdominal wall. A stoma may be temporary or permanent, may be needed in any age group and may be sited on any part of the abdomen. The specific digestive pathology that could have as result of the surgical management a stoma is represented by colon, rectal and anal cancer, diverticular disease of the colon and rectum, Crohn's disease, ischaemic bowel, volvulus, trauma, Hirschprung disease, imperforate anus, fecal incontinence. This paper aim is to asses the management of fecal stomas and the necessity of a trained ostomy support team.

[Malignant peritoneal mesothelioma tumours. Evolution, treatment, prognosis]

Malignant mesothelioma of the peritoneum is a rare neoplasm with a rapidly fatal course. The median survival range is from 5 to 12 months in untreated cases with little improvement seen in patients receiving multimodality therapy. Although most cases occur in the fifth and sixth decades, peritoneal mesothelioma can be seen in any age group. Approximately 30% of all mesotheliomas arise solely from the peritoneum. Asbestos exposure, primarily of the crocidolite variety, has been implicated in the pathogenesis of this malignancy, as was established in South Africa in the 1960s. Half of reported cases have a history of asbestos exposure. The diagnosis of peritoneal mesothelioma is often delayed, in part because of the usually long latent period (peaking at 40-45 years from the time of initial exposure to asbestos) and because the common presenting symptoms of weight loss, usually with a full abdomen, malaise, and abdominal discomfort, are mild and nonspecific. This paper aim is to present a case report regarding a patient diagnosed with malignant peritoneal mesothelioma with an unpredictable evolution.

Femtosecond electron and spin dynamics in Gd(0001) studied by time-resolved photoemission and magneto-optics

Femtosecond electron and spin dynamics of the Gd(0001) surface are investigated by time-resolved photoemission and second harmonic generation. Upon optical excitation the spin polarization of the surface state is reduced by half while its exchange splitting remains nearly unchanged. Electron-magnon interaction is proposed to facilitate electron-spin-flip scattering among spin-mixed surface and bulk states, which provides a mechanism for ultrafast demagnetization.

A rare case of glioblastoma multiforme

A male, 39 years, entered rapidly in coma, was admitted in the Neurological Hospital Brasov and deceased after 4 hrs in hospital. At necropsy, macroscopic appearances of the cut surface showing unique tumour mass in all brain from frontal lobe to cerebellum, with extensive cortical invasion. The tumor has a variable coloration, a yellowish central necrosis and cysts containing turbid fluid. Histopathological aspect is extremely variable with regional heterogeneity: striking cellular pleomorphism with a lack of cell processes, anaplastic glial cells, and some multinucleated giant cells, large necrotic areas with pseudo-palisading of surrounding tumor cells and microvascular proliferation, as glomeruloid tufts.

[Use of polypropylene mesh for incisional hernia repair]

Incisional hernia is an important complication of abdominal surgery. Procedures for the repair of these hernias with sutures and with mesh have been reported, but there is no consensus about which type of procedure is best. We have performed a retrospective analysis on 1014 patients operated on in our unit between 1994 and 2003 for simple or recurrent incisional hernias. The polypropylene mesh has been used in a number of 107 patients. The mesh has been placed either intraperitoneal, extraperitoneal/subfascial or onlay. Median follow-up was 36 months. There were 1 enterocutaneous fistula and 5 wound sinus developed. The mesh had to be removed in 6 cases. All of these complication developed when the mesh has been placed either extraperitoneal/subfascial or onlay. We note 5 recurrent incisional hernias after a period of up to 24 months. The recurrence rates after open mesh repair are less then after primary closure. The intraperitoneal use of polypropylene mesh with omental coverage is a good procedure with less complications.

[Anterior resection of the rectum for rectal cancer--options, limits, immediate complications]

A number of factors have recently led to a more conservative approach for middle or low rectal cancers, making possible sphincter preservation and reducing the number of abdomino perineal excisions of the rectum. We have performed a retrospective analysis on 510 patients operated on in our unit between 1994 and 2003 for rectal cancer. There were a number of 118 anterior resection of rectum; in 20 cases the TME has been performed and in 6 cases a very low anterior resection of rectum was done. The overall operative morbidity rate was 16.10% in direct relation with the distal limit of resection. We note urinary dysfunctions, anastomotic leakage, recto-vaginal fistulas as immediate postoperative complications. With the practice of total mesorectal excision, the use of abdomino perineal excision of the rectum is decreasing. The use of preoperative radiotherapy can increase the rate of operative morbidity but despite of these, its long-term benefit, is important.

Photoreactions of Metarhodopsin III

Meta III is an inactive intermediate thermally formed following light activation of the visual pigment rhodopsin. It is produced from the Meta I/Meta II photoproduct equilibrium of rhodopsin by a thermal isomerization of the protonated Schiff base C=N bond of Meta I, and its chromophore configuration is therefore all-trans 15-syn. In contrast to the dark state of rhodopsin, which catalyzes exclusively the cis to trans isomerization of the C11=C12 bond of its 11-cis 15-anti chromophore, Meta III does not acquire this photoreaction specificity. Instead, it allows for light-dependent syn to anti isomerization of the C15=N bond of the protonated Schiff base, yielding Meta II, and for trans to cis isomerizations of C11=C12 and C9=C10 of the retinal polyene, as shown by FTIR spectroscopy. The 11-cis and 9-cis 15-syn isomers produced by the latter two reactions are not stable, decaying on the time scale of few seconds to dark state rhodopsin and isorhodopsin by thermal C15=N isomerization, as indicated by time-resolved FTIR methods. Flash photolysis of Meta III produces therefore Meta II, dark state rhodopsin, and isorhodopsin. Under continuous illumination, the latter two (or its unstable precursors) are converted as well to Meta II by presumably two different mechanisms.

Consequences of Counterion Mutation in Sensory Rhodopsin II ofNatronobacterium pharaonisfor Photoreaction and Receptor Activation: An FTIR Study

In many retinal proteins the proton transfer from the Schiff base to the counterion represents a functionally important step of the photoreaction. In the signaling state of sensory rhodopsin II from Natronobacterium pharaonis this transfer has already occurred, but in the counterion mutant Asp75Asn it is blocked during all steps of the photocycle. Therefore, the study of the molecular changes during the photoreaction of this mutant should provide a deeper understanding of the activation mechanism, and for this, we have applied time-resolved step-scan FTIR spectroscopy. The photoreaction is drastically altered; only red-shifted intermediates are formed with a chromophore strongly twisted around the 14-15 single bond. In addition, the photocycle is shortened by 2 orders of magnitude. Nevertheless, a transition involving only protein changes similar to that of the wild type is observed, which has been correlated with the formation of the signaling state. However, whereas in the wild type this transition occurs in the millisecond range, it is shortened to 200 micros in the mutant. The results are discussed with respect to the altered electrostatic interactions, role of proton transfer, the published 3D structure, and physiological activity.

Coherent optical phonons and parametrically coupled magnons induced by femtosecond laser excitation of the Gd(0001) surface

Coherent spin dynamics in the THz domain coupled to a coherent phonon is observed in the time-resolved second harmonic response of the Gd(0001) ferromagnetic metal surface. An LO phonon of 2.9 THz is excited by a transient charge displacement at the surface caused by resonant absorption of a fs laser pulse in the exchange-split surface state. This lattice vibration modulates the interlayer distance inducing a coherent variation of the exchange interaction between spins in adjacent layers. The resulting magnetization dynamics is considered as optical magnon wave packets coupled to the phonon.

Double immunolabeling of neuropeptides in the human hypothalamus as analyzed by confocal laser scanning fluorescence microscopy

The main goal of this study was to develop a better light microscopic procedure for quantitative study of the cellular co-localization of neuropeptides in adult human brain tissue. To reach this goal, we opted for a method (proved to be optimal on rat brain) in which sections were double immunolabeled with two different fluorophore-conjugated secondary antibodies and analyzed with a confocal laser scanning fluorescence microscope. One of our main problems faced was a strong autofluorescence of the sections, mainly caused by lipofuscin granules normally present in adult human brain tissue, which made any analysis of specific fluorescence impossible. This problem could be solved by staining the sections after immunolabeling with the dye Sudan Black B, which completely blocked this autofluorescence. The complete optimized procedure that we eventually developed can be summarized as follows. After a relatively short fixation time (6-14 days) in 4% freshly depolymerized paraformaldehyde, the resected brain tissue can best be stored in a 30% sucrose solution supplemented with 0.05% NaN3 at 4C. Stored under these conditions, cryosections from the tissue still reveal good histology and allow successful immunocytochemical staining after a period of 6 months. Double immunolabeling is done by incubating cryo- or paraffin sections in a mixture of two primary antibodies directed against the targeted antigens, followed by incubation with two different fluorophore-conjugated secondary antibodies. Amplification with a biotinylated secondary antibody followed by fluorophore-conjugated streptavidin is possible. Finally, the sections are stained with Sudan Black B, mounted in plain 80% Tris-buffered glycerol, and studied by confocal laser scanning fluorescence microscopy. Sections processed in this way are well suited for qualitative and quantitative analyses of co-localized neuropeptides in human brain tissue.

Aspects of 1,25-dihydroxyvitamin D3 binding sites in fish: an autoradiographic study

The distribution of specific binding sites for vitamin D3 in adult female and male Xiphophorus helleri is studies after injection of tritiated 1,25-dihydroxyvitamin D3 (vitamin D) by thaw-mount autoradiography. Five hours after injection of labeled vitamin D specific nuclear binding is present in brain, pituitary, skin, gills, cartilage, gut, liver, pancreas, spleen, kidney, muscle, ovary, and testis. Cytoplasmic binding exists strongest in gills, gut, and kidney while it is comparatively weak in hepatocytes. In reproductive organs cytoplasmic retention of radioactivity is also present in oocytes. Weak nuclear labeling exists in interstitial cells in ovary. Conspicuous nuclear labeling exists in active lobules of testis, while inactive lobules show occasionally a few labeled cells. The results demonstrate specific binding and retention of vitamin D in many target organs of teleost fish, suggesting an extensive and multifunctional regulatory role of this steroid hormone of sunlight.

Immunohistochemical aspects of chromogranins in endocrine cells of the duodenal mucosa in some primates

Endocrine cells in the duodenal mucosa of some primates (Cercopithecus aetiops, Macaca cinomolgus-nemestrina and Macaca rhesus) have been studied with immunohistochemical methods for chromogranins. Material sampling immediately after death (by carotid bleeding concomitantly with formalin 10% perfusion) was helpful in the study of endocrine cells. The location and number of endocrine cells of the duodenal mucosa of the primates under study are generally similar to those of humans. The use of an antibody cocktail against all three Cgs/Sgs appears to be the method of choice to identify neuroendocrine granule-containing cells. When comparing the results of this study with those obtained by us in a previous work by silver staining, the Grimelius technique is recommended together with the immunohistochemical techniques for chromogranins in the practice of the usual diagnosis of the endocrine pathology.