Changes in angiotensin II receptors in dopamine-rich regions of the mouse brain with age and ethanol consumption

The density of angiotensin II (Ang II) receptors was determined in three dopaminergic nerve terminal-rich brain regions (caudate putamen, nucleus accumbens, and ventral pallidum) of mice that were given either water (control) or 20% w/v ethanol (EtOH) to drink for either 2-8 weeks (young) or 46 weeks (old). The receptors were labeled with 125I-sarcosine1, isoleucine8 angiotensin II (125I-SI Ang II) and measured by quantitative densitometric image analysis (receptor autoradiography) or by saturation binding assays on homogenates of these brain regions. The selective AT2 receptor subtype antagonist PD 123319 (10 microM) was used to inhibit 125I-SI Ang II binding to AT2 receptors to determine AT1 receptor density in brain sections. In young control mice the density of Ang II receptor binding sites in the caudate putamen was 407+/-26 fmol/g, in the nucleus accumbens the density was 346+/-27 fmol/g, and in the ventral pallidum the density was 317+/-27 fmol/g. Less than 5% of specific 125I-SI Ang II binding was displaced by PD 123319, suggesting that nearly all of the Ang II receptors in these brain regions were the AT1 subtype. The Bmax in homogenates of these three regions in young control mice was 11.0+/-2.1 fmol/mg protein. The KD was 0.49+/-0.13. Ang II receptors in old mouse brains were decreased, respectively, by 32%, 35% and 30% in the caudate putamen, nucleus accumbens and ventral pallidum (p<0.001). Ang II receptors were slightly, but not significantly increased in both young and old EtOH-consuming mice.

Involvement of protein kinase C in the nitric oxide-mediated peripheral nerve disturbance in endotoxemic rats

The role of protein kinase C (PKC) in nitric oxide (NO)-mediated peripheral nerve disturbance in lipopolysaccharide (endotoxin, LPS)-treated rat was studied. The impaired Na+,K+ -ATPase activities in sciatic nerves from LPS-treated rats were prevented by aminoguanidine (NO synthase inhibitor) and corrected by PKC agonist in vitro. Using Western blot to determine PKC isoforms alpha and beta polypeptide levels in LPS-treated rat sciatic nerves, we found that alpha isoform was markedly reduced in the particulate fraction, but the beta isoform was unaffected. The alpha and beta isoforms in the cytosolic fractions were not significantly different as compared with control. This diminished particulate PKC alpha isoform was prevented by the treatment of aminoguanidine. Moreover, the motor nerve conduction velocity was significantly reduced in endotoxemic rats and corrected by aminoguanidine. These results indicate that the alteration of PKC alpha isoform in Na+,K+ -ATPase-enriched fraction of sciatic nerve may be related to the NO-mediated peripheral nerve disturbance in endotoxemic rats.

Treatment of duck hepatitis B virus by antisense poly-2'-O-(2,4-dinitrophenyl)-oligoribonucleotides

The poly-2'-O-(2,4-dinitrophenyl)-oligoribonucleotide (poly-DNP-RNA) with antisense sequence 5'ggguguauggaaaagccguc-3' was designed to target the sequence 2468-2487 in the polymerase gene of duck hepatitis B virus (DHBV). The stereochemically pure RNA was synthesized by using T7 RNA polymerase with synthetic DNA template and subsequently derivatized with 2,4-dinitrofluorobenzene in mild basic conditions to make the poly-DNP-RNA with an average DNP/base ratio of 0.7. In vitro studies showed that this antisense poly-DNP-RNA can hybridize with sense DNA and has high resistance to RNase A digestion. These poly-DNP-RNA were also found to be potent sequence-independent inhibitors of the reverse transcriptase activity of DHBV DNA-polymerase. For in vivo studies, DHBV-infected ducks were treated with antisense, sense, and random noncomplementary sequence poly-DNP-RNA, respectively. The data showed that the antisense poly-DNP-RNA completely inhibited the duck viremia in all nine ducks that had been treated with a dose of 1 mg/kg (i.v.) per day for 25 days. The viremia did not come back after 10 months recession. In the sense group, three of the four ducks showed no inhibition, and in the random group, both ducks maintained their viremia. After 45 days of treatment with the antisense poly-DNP-RNA, followed by 2 weeks of recession, PCR as well as QC-PCR assay and microscopic examination showed that viral DNA had disappeared in liver and that the histology of the damaged liver (filled with fat granules) had returned to normal.

Synthesis of large arrays of well-aligned carbon nanotubes on glass

Free-standing aligned carbon nanotubes have previously been grown above 700 degreesC on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666 degreesC by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0. 1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication.

Nitric oxide mediates hepatocyte injury

The degree of acute hepatic failure after severe trauma and sepsis is related to the extent of hepatocyte (HC) damage and cell death resulting from either necrosis or apoptosis. We have previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide (LPS) can directly lead to HC necrosis, but not apoptosis. To date, the reactive oxygen intermediates (ROI) and nitric oxide (NO) have been shown to play a potential role in the induction of cell apoptosis. However, it is unknown whether ROI and NO are involved in HC cell death. Therefore, in this study we tested the hypothesis that NO and ROI exert different effects on HC cell death. TNF-alpha and LPS alone failed to induce HC apoptosis but when combined with antioxidants resulted in HC apoptosis and DNA fragmentation, which is correlated with an increase in NO production. This effect was attenuated by the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). Moreover, the NO donor sodium nitroprusside resulted in HC apoptosis and cell damage as represented by hepatocellular enzyme release. Antioxidants inhibited TNF-alpha- and LPS-mediated ROI generation and peroxynitrite formation in HC. TNF-alpha- and LPS-induced HC damage could be further reduced by the combination of antioxidants and L-NMMA. These results indicate that NO is involved in HC injury, primarily through the induction of HC apoptosis.

Aiolos regulates B cell activation and maturation to effector state

Aiolos encodes a zinc finger DNA-binding protein that is highly expressed in mature B cells and is homologous to Ikaros. In the periphery of mice homozygous for an Aiolos-null mutation, B cells exhibit an activated cell surface phenotype and undergo augmented antigen receptor (BCR)-mediated in vitro proliferative responses, even at limiting amounts of stimulant. In vivo, T cell-dependent B cell responses, including the formation of germinal centers and elevated serum IgG and IgE, are detected in Aiolos-deficient mice in the absence of immunization. Auto-antibodies and development of B cell lymphomas are frequently seen among aging Aiolos mutants. In sharp contrast to conventional B cells, B cells of the peritoneum, of the marginal zone, and the recirculating bone marrow population are greatly reduced.

Structural basis of CD8 coreceptor function revealed by crystallographic analysis of a murine CD8alphaalpha ectodomain fragment in complex with H-2Kb

The crystal structure of the two immunoglobulin variable-like domains of the murine CD8alphaalpha homodimer complexed to the class I MHC H-2Kb molecule at 2.8 A resolution shows that CD8alphaalpha binds to the protruding MHC alpha3 domain loop in an antibody-like manner. Comparison of mouse CD8alphaalpha/H-2Kb and human CD8alphaalpha/HLA-A2 complexes reveals shared as well as species-specific recognition features. In both species, coreceptor function apparently involves the participation of CD8 dimer in a bidentate attachment to an MHC class I molecule in conjunction with a T cell receptor without discernable conformational alteration of the peptide or MHC antigen-presenting platform.

MR findings of renin-secreting tumor: a case report

The renin-secreting tumor is a rare benign tumor of the kidney. It is usually detected in young hypertensive patients with high plasma renin activity and hypokalemia. We describe the magnetic resonance findings of a case of renin-secreting tumor of the kidney.

Supercritical fluid extraction and off-line clean-up for the analysis of organochlorine pesticide residues in garlic

An approach using supercritical fluid extraction (SFE) followed by clean-up with a AgNO3-loaded Florisil column was utilized for the analysis of four organochlorine pesticides (OCPs) in garlic. The organic sulfur extracted by SFE from garlic was removed by AgNO3 allowing OCPs to be determined by GC-electron-capture detection without interferences. All OCPs recoveries ranged from 85.0% to 110.0% and relative standard deviations were in the range of 3.9-7.2% for spiked samples. The described method may be used to analyze OCPs in garlic on a routine basis.

Vibrational study of phosphate modes in GDP and GTP and their interaction with magnesium in aqueous solution

Raman and infrared spectra were examined for guanosine 5'-diphosphate (GDP) and guanosine 5'-triphosphate (GTP) in aqueous solution. The vibrational modes were assigned on the basis of isotopic frequency shifts and relative intensities in the Raman and infrared spectra. The observed frequency shifts on 18O isotope labeling made it possible to identify the bands from each phosphate group (alpha, beta, gamma). Frequency shifts were observed as Mg2+ complexes with GDP and GTP. The results suggested that Mg2+ binds to GDP in a bidentate manner to the alpha, beta P[symbol: see text]O bonds and in a tridentate manner to the alpha, beta and gamma P[symbol: see text]O bonds of Mg.GTP. The results indicate that structure of Mg2+ coordinated to GTP in aqueous solution differs somewhat to that found for Mg.ATP.

Differential thymic selection outcomes stimulated by focal structural alteration in peptide/major histocompatibility complex ligands

The T lineage repertoire is shaped by T cell receptor (TCR)-dependent positive and negative thymic selection processes. Using TCR-transgenic (N15tg) beta2-microglobulin-deficient (beta2m-/-) RAG-2(-/-) H-2(b) mice specific for the VSV8 (RGYVYQGL) octapeptide bound to Kb, we identified a single weak agonist peptide variant V4L (L4) inducing phenotypic and functional T cell maturation. The cognate VSV8 peptide, in contrast, triggers negative selection. The crystal structure of L4/Kb was determined and refined to 2.1 A for comparison with the VSV8/Kb structure at similar resolution. Aside from changes on the p4 side chain of L4 and the resulting alteration of the exposed Kb Lys-66 side chain, these two structures are essentially identical. Hence, a given TCR recognizes subtle distinctions between highly related ligands, resulting in dramatically different selection outcomes. Based on these finding and the recent structural elucidation of the N15-VSV8/Kb complex, moreover, it appears that the germ-line Valpha repertoire contributes in a significant way to positive selection.

Raman difference studies of GDP and GTP binding to c-Harvey ras

The vibrational spectra of phosphate modes for GDP and GTP bound to the c-Harvey p21(ras) protein have been determined using 18O isotope edited Raman difference spectroscopy. A number of the phosphate stretch frequencies are changed upon GDP/GTP binding to ras, and the results are analyzed by ab initio calculations and through the use of empirical relationships that relate bond orders and bond lengths to vibrational frequencies. Bound GDP is found to be strongly stabilized by its interactions, mostly electrostatic, with the active site Mg2+. Bound GTP also interacts with the active site Mg2+ via its beta-phosphate group, as expected on the basis of crystallographic studies of bound GppNp. The angle between the nonbridging P&bondDot;O bonds of the gamma-phosphate of bound GTP increase by about 1-2 degrees compared to its solution value, thus bringing about a geometry that is closer to planar for these bonds as expected for the putative pentacoordinated transition state geometry of the phosphotransfer reaction. Modeling of the interactions at the nucleotide binding site suggests that the water molecule in-line with the P-O bond is positioned to bring about the change in bond angle. Moreover, a weak fifth bond (about 0.03 vu) appears to be formed between it and the gamma-phosphorus atom of bound GTP with a concomitant weakening of the O-P bond between the GDP leaving group and the gamma-phosphorus atom. Hence, an important role of the active site structure appears to be the strategic positioning of this in-line water. These structural results are consistent with a reaction pathway for GTP hydrolysis in ras of synchronous bond formation between the gamma-phosphorus of GTP and the attacking nucleophile and bond breaking between the gamma-phosphorus and the GDP leaving group.

Extremely high prevalence of nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among children in Kaohsiung, Taiwan

Resistance (intermediate and high) to penicillin among Streptococcus pneumoniae strains is an emerging problem worldwide. From 1995 to 1997, isolates of S. pneumoniae not susceptible to penicillin were seen with increasing frequency from blood, cerebrospinal fluid, pleural fluid, and middle ear fluid from pediatric patients at the Veterans General Hospital-Kaohsiung. To determine the prevalence of carriage of these penicillin-nonsusceptible S. pneumoniae isolates, we obtained nasopharyngeal swab specimens from 2,905 children (ages, 2 months to 7 years) attending day-care centers or kindergartens or seen in our outpatient clinic. S. pneumoniae was isolated from 611 children, and 584 strains were available for analysis. The oxacillin disc test was used as a screening test to evaluate penicillin susceptibility. The MICs of 11 antibiotics (penicillin, cefaclor, cefuroxime, ceftriaxone, cefotaxime, imipenem, chloramphenicol, clarithromycin, rifampin, vancomycin, and teicoplanin) were determined by the E-test. Only 169 (29%) of the strains were susceptible to penicillin; 175 (30%) strains were intermediately resistant and 240 (41%) were highly resistant. The isolates also demonstrated high rates of resistance to other beta-lactams (46% were resistant to cefaclor, 45% were resistant to cefuroxime, 45% were resistant to ceftriaxone, 31% were resistant to cefotaxime, and 46% were resistant to imipenem). The rate of resistance to macrolide antimicrobial agents was strikingly high; 95% of the isolates were not susceptible to clarithromycin. However, 97% were susceptible to rifampin and 100% were susceptible to the two glycopeptides (vancomycin and teicoplanin). While reports of penicillin-resistant S. pneumoniae increased worldwide through the 1980s, the high prevalence (71%) of resistance reported here is astonishing. Surveillance of nasopharyngeal swab specimen cultures may provide useful information on the prevalence of nonsusceptible strains causing invasive disease. Such information could be used to guide therapy of pneumococcal infections.

The structure of immunoglobulin superfamily domains 1 and 2 of MAdCAM-1 reveals novel features important for integrin recognition

BACKGROUND

Mucosal addressin cell adhesion molecule 1 (MAdCAM-1) is a cell adhesion molecule that is expressed on the endothelium in mucosa, and guides the specific homing of lymphocytes into mucosal tissues. MAdCAM-1 belongs to a subclass of the immunoglobulin superfamily (IgSF), the members of which are ligands for integrins. Human MAdCAM-1 has a unique dual function compared to other members in the same subclass in that it binds both the integrin alpha4beta7, through its two IgSF domains, and a selectin expressed on leukocytes, via carbohydrate sidechains. The structure determination of the two IgSF domains and comparison to the N-terminal two-domain structures of vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecules (ICAM-1 and ICAM-2) allow us to assess the molecular basis of the interactions between integrins and their preferred ligands.

RESULTS

The crystal structure of a fragment containing the two IgSF domains of human MAdCAM-1 has been determined to 2.2 A resolution. The structure of MAdCAM-1 reveals two separate integrin-recognition motifs. The key integrin-binding residue, Asp42, resides in the CD loop of domain 1; a buried arginine residue (Arg70) plays a critical role in maintaining the conformation of this loop. The second binding site is associated with an unusual long D strand in domain 2. The D and E strands extend beyond the main body of the domain, forming a negatively charged beta ribbon unique to MAdCAM-1. This ribbon is located on the same face as the key aspartate residue in domain 1, consistent with evidence that it is involved in integrin binding.

CONCLUSIONS

The structural comparison of MAdCAM-1 to other members of the same IgSF subclass reveals some interesting features. Firstly, MAdCAM-1, like VCAM-1, has the key integrin-binding residue located on the protruding CD loop of domain 1 and binds to an integrin that lacks an I domain. This is in contrast to ICAM-1 and ICAM-2 where the key residue is located at the end of the C strand on a flat surface and which bind to integrins that contain I domains. Secondly, architectural differences in the CD loops of MAdCAM-1 and VCAM-1 cause an 8 A shift in position of the critical aspartate residue, and may partly determine their binding preference for different integrins. Finally, the unusual charge distribution of the two-domain fragment of MAdCAM-1 is predicted to orient the molecule optimally for integrin binding on the top of its long mucin-like stalk.

[Septicemic melioidosis in Southern Taiwan: a case report]

The patient was a 56 year-old man, a resident of Hen-Tsueng Township in Ping-Tung County. He worked as a ranger at Ken-Ting Farm in southern Taiwan, and had been to Thailand for sight-seeing 5 years ago. He came to our outpatient department about one month prior to hospitalization for intermittent fever of one week duration. At that time, complete blood count was within normal limits and a chest roentgenogram was unremarkable. He was given erythromycin without showing any clinical improvement. Two days prior to admission, he noted pain in the left hip. The next day, severe dyspnea developed suddenly and chest x-ray film revealed bilateral nodular lesions. Physical examination on hospitalization revealed an acutely ill and jaundiced male with a temperature of 37.4 degrees C, blood pressure: 110/47 mmHg, pulse rate: 137/min, and respiratory rate: 26/min. There were rales in both lungs, but no lymphadenopathy or organ enlargement. Laboratory study showed WBC: 1,470/mm(3), platelet count: 47,000/mm(3), blood sugar: 226 mg/dL, mildly elevated transaminases and bilirubin, and BUN: 69 mg/dL, Cr: 4.3 mg/dL. Arterial blood gas analysis indicated an acute metabolic acidosis with PaO2 of 32 mmHg. Despite the initial impression of melioidosis and administration of ceftazidime plus gentamicin, his condition rapidly deteriorated and expired 18 hours after admission. Two sets of blood cultures grew Burkholderia pseudomallei. Melioidosis has been called a great imitator of diseases and culture results are frequently misinterpreted. The mortality is high even with suggested therapy with ceftazidime, cotrimoxazole, amoxicillin-clavulanate, chloramphenicol, and/or tetracycline. There has been a total of 10 cases reported in southern Taiwan and 2 of them were clearly indigenous. Melioidosis should be included in the reportable diseases, and its prevalence in Taiwan also should be investigated.

Primary liver abscess due to Klebsiella pneumoniae in Taiwan

Pyogenic liver abscess is an uncommon complication of intra-abdominal or biliary tract infection and is usually a polymicrobial infection associated with high mortality and high rates of relapse. However, over the past 15 years, we have observed a new clinical syndrome in Taiwan: liver abscesses caused by a single microorganism, Klebsiella pneumoniae. We reviewed 182 cases of pyogenic liver abscess during the period September 1990 to June 1996; 160 of these cases were caused by K. pneumoniae alone, and 22 were polymicrobial. When patients with K. pneumoniae liver abscess were compared with those who had polymicrobial liver abscess, we found higher incidences of diabetes or glucose intolerance (75% vs. 4.5%) and metastatic infections (11.9% vs. 0) and lower rates of intra-abdominal abnormalities (0.6% vs. 95.5%), mortality (11.3% vs. 41%), and relapse (4.4% vs. 41%) in the former group. Liver abscess caused by K. pneumoniae is a new clinical syndrome that has emerged as an important infectious complication in diabetic patients in Taiwan.

Effect of i.v. glucose versus combined i.v. plus oral glucose on human tumour extracellular pH for potential sensitization to thermoradiotherapy

The purpose of this study was to determine whether intravenous or combined intravenous plus oral glucose administration was more effective inducing acute tumour acidification. Seventeen nondiabetic patients at the Henan Tumour Hospital with superficial tumour deposits of various histologies and size were administered, after fasting, either 50 g glucose intravenously (i.v., in 100 ml over 10 min) or 50 g i.v. glucose (in 100 ml over 10 min) combined with 100 g oral glucose (in 200 ml; i.v. + oral). Extracellular tumour pH (pHe) was determined with one or two indwelling needle combination pH microelectrodes. Blood glucose concentration was determined every 15-20 min by finger stick with Chem-Strips and a Glucometer. Ten patients received i.v. glucose, and seven patients received i.v. + oral glucose. Blood glucose rose to 430 +/- 15 mg/dL in both groups. However, the rate of clearance of blood glucose was greater for the i.v. glucose than for the i.v. + oral glucose group (p < 0.00002), and thus the blood glucose levels remained elevated longer after i.v. + oral than after i.v. glucose administration. Relative to the initial fasting blood glucose concentration, blood glucose was -2 +/- 7 mg/dL at 110 min after glucose administration by the i.v. route, whereas, blood glucose relative to initial values was 143 + 23 mg/dL by 110 min after glucose administration by the i.v. + oral route, p = 0.000004. The initial pHe values in the two groups of tumours were similar, 7.34 +/- 0.09 (6.78-7.71) and 7.35 +/- 0.08 (6.99-7.61), respectively. After i.v. glucose, tumour acidification occurred in nine of ten patients (-0.16 + 0.02 pH unit, range -0.24 to -0.05), and after i.v. + oral glucose tumour acidification occurred in six of seven patients (-0.19 +/- 0.07 pH unit, range -0.43 to -0.06). When the initial fasting blood glucose concentration was in excess of 82 mg/dL, all patients (12/12) exhibited tumour acidification during hyperglycaemia, whereas, only 3/5 patients exhibited tumour acidification when the initial blood glucose concentration was less than 82 mg/dL (p = 0.07). The time to maximum decrease in tumour pHe was significantly shorter after i.v. + oral glucose than after i.v. glucose (e.g., 67 +/- 11 versus 102 +/- 8 min, p = 0.02) and correlated with the rate of clearance of blood glucose (p = 0.02, r = 0.55). Larger tumours tended to exhibit a greater decrease in pHe (p = 0.08, r = 0.04). The only side effects of hyperglycaemia were transient nausea and increased urinary output. The effect of hyperglycaemia induced by administration of 200 g oral glucose was similar to i.v. administration in that 83% of tumours exhibited acidification of 0.14 +/- 0.02 pH unit by 91 +/- 7 min. We conclude that i.v. and i.v. + oral glucose administration are equally effective inducing tumour acute acidification, but no more effective than 200 g oral glucose, for investigation of hyperglycemic sensitization to thermoradiotherapy.

Prostate cancer: local staging with endorectal magnetic resonance imaging

BACKGROUND

Prostate cancer has received increasing attention during the past decades. Staging of tumors before treatment is imperative for planning appropriate therapy. The purpose of this study is to assess the role of endorectal magnetic resonance imaging (MRI) in local staging of prostate cancer.

METHODS

Endorectal MRI was performed in 31 patients with histologically-proven prostate cancer. MRI was done three to 100 days (mean, 32.1 days) after either transrectal ultrasonography (TRUS) with biopsy or transurethral resection of the prostate (TURP). Radical prostatectomies were performed within two weeks after MRI. The diagnostic accuracy of endorectal MRI for local tumor staging, specifically for extracapsular extension (ECE) and seminal vesicle invasion (SVI), was evaluated by correlating MRI results with histopathologic findings of whole-mount specimens.

RESULTS

The accuracy of endorectal MRI for the detection of tumor presence and estimation of tumor volume was 48%. Sensitivity, specificity and positive predictive value for evaluation of ECE were 88%, 69% and 80%, respectively, and for SVI, were 66%, 84% and 50%, respectively. The overall accuracy of MRI in local tumor staging (using the TMN system) was 61%. Accuracy in differentiating localized from invasive cancer was 84%.

CONCLUSION

Endorectal MRI is not accurate enough to detect tumor presence or estimate tumor volume. Diagnostic accuracy for local tumor staging is unsatisfactory. However, endorectal MRI is highly accurate in differentiating localized (stage B) from invasive (stage C) cancer.

A dimeric crystal structure for the N-terminal two domains of intercellular adhesion molecule-1

The 3.0-A structure of a 190-residue fragment of intercellular adhesion molecule-1 (ICAM-1, CD54) reveals two tandem Ig-superfamily (IgSF) domains. Each of two independent molecules dimerizes identically with a symmetry-related molecule over a hydrophobic interface on the BED sheet of domain 1, in agreement with dimerization of ICAM-1 on the cell surface. The residues that bind to the integrin LFA-1 are well oriented for bivalent binding in the dimer, with the critical Glu-34 residues pointing away from each other on the periphery. Residues that bind to rhinovirus are in the flexible BC and FG loops at the tip of domain 1, and these and the upper half of domain 1 are well exposed in the dimer for docking to virus. By contrast, a residue important for binding to Plasmodium falciparum-infected erythrocytes is in the dimer interface. The presence of A' strands in both domains 1 and 2, conserved hydrogen bonds at domain junctions, and elaborate hydrogen bond networks around the key integrin binding residues in domain 1 make these domains suited to resist tensile forces during adhesive interactions. A subdivision of the intermediate (I) set of IgSF domains is proposed in which domain 1 of ICAM-1 and previously described I set domains belong to the I1 set and domain 2 of ICAM-1, ICAM-2, and vascular cell adhesion molecule-1 belong to the I2 set.

Identification of a common docking topology with substantial variation among different TCR-peptide-MHC complexes

Whether T-cell receptors (TCRs) recognize antigenic peptides bound to major histocompatability complex (MHC) molecules through common or distinct docking modes is currently uncertain. We report the crystal structure of a complex between the murine N15 TCR [1-4] and its peptide-MHC ligand, an octapeptide fragment representing amino acids 52-59 of the vesicular stomatitis virus nuclear capsid protein (VSV8) bound to the murine H-2Kb class I MHC molecule. Comparison of the structure of the N15 TCR-VSV8-H-2Kb complex with the murine 2C TCR-dEV8-H-2Kb [5] and the human A6 TCR-Tax-HLA-A2 [6] complexes revealed a common docking mode, regardless of TCR specificity or species origin, in which the TCR variable Valpha domain overlies the MHC alpha2 helix and the Vbeta domain overlies the MHC alpha1 helix. As a consequence, the complementary determining regions CDR1 and CDR3 of the TCR Valpha and Vbeta domains make the major contacts with the peptide, while the CDR2 loops interact primarily with the MHC. Nonetheless, in terms of the details of the relative orientation and disposition of binding, there is substantial variation in TCR parameters, which we term twist, tilt and shift, and which define the variation of the V module of the TCR relative to the MHC antigen-binding groove.