| 1. |
- Adloff, C, et al.
(författare)
-
Diffractive photoproduction of psi(2S) mesons at HERA
- 2002
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 541:3-4, s. 251-264
-
Tidskriftsartikel (refereegranskat)abstract
- Results on diffractive photoproduction of psi(2S) mesons are presented using data collected between 1996 and 2000 with the H1 detector at the HERA ep collider. The data correspond to an integrated luminosity of 77 pb(-1). The energy dependence of the diffractive psi(2S) cross section is found to be similar to or possibly somewhat steeper than that for J/psi mesons. The dependences of the elastic and proton dissociative psi(2S) photoproduction cross sections on the squared momentum transfer t at the proton vertex are measured. The t-dependence of the elastic channel, parametrised as e(bt), yields b(el)(psi(2S)) = (4.31 +/- 0.57 +/- 0.46) GeV-2, compatible with that of the J/psi. For the proton dissociative channel the result b(pd)(psi(2S)) = (0.59 +/- 0.13 +/- 0.12) GeV-2 is 2.3 standard deviations smaller than that measured for the J/psi. With proper account of the individual wavefunctions theoretical predictions based on perturbative QCD are found to describe the measurements well. (C) 2002 Elsevier Science B.V. All rights reserved.
|
|
| 2. |
- Adloff, C, et al.
(författare)
-
Inelastic photoproduction of J/psi mesons at HERA
- 2002
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 25:1, s. 25-39
-
Tidskriftsartikel (refereegranskat)abstract
- An analysis of inelastic photoproduction of J/psi mesons is presented using data collected at the ep collider HERA corresponding to an integrated luminosity of above 80 pb(-1), Differential and double I < P-t/psi(2) < differential cross sections are measured in a wide kinematic region: 60 < W-gammap < 260 GeV, 1 p(t,psi)(2) < 60 GeV2 and 0.05 < z < 0.9. where z is the fraction of the energy of the exchanged photon transferred to the J/psi meson in the rest frame of the target proton. Cross sections at z less than or similar to 0.3 are presented for the first time. Theoretical calculations within the Colour Singlet Model at NLO for direct photon processes are shown to give a good description of the data in the medium z region (0.3 < z < 0.9) up to the highest p(t,psi)(2) values. A calculation using a k(t) factorisation approach in LO in the Colour Singlet Model is also able to describe these data. The data in the full z range are also compared to LO calculations within a non-relativistic QCD framework including colour octet and colour singlet contributions for direct and resolved photons. It seems possible to reconcile data and theory with modest contributions from colour octet processes. The polarisation of the J/psi meson is measured as a function of z and p(t,psi) and is reasonably described by the theoretical predictions.
|
|
| 3. |
- Adloff, C, et al.
(författare)
-
Measurement and QCD analysis of neutral and charged current cross sections at HERA
- 2003
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 30:1, s. 1-32
-
Tidskriftsartikel (refereegranskat)abstract
- The inclusive e(+)p single and double differential cross sections for neutral and charged current processes axe measured with the H1 detector at HERA. The data were taken in 1999 and 2000 at a centre-of-mass energy of roots = 319 GeV and correspond to an integrated luminosity of 65.2 pb(-1). The cross sections are measured in the range of four-momentum transfer squared Q(2) between 100 and 30 000 GeV2 and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e(+)p data and the earlier e-p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function F-L at high Q(2) (110 - 700 GeV2). A new measurement of the structure function x (F) over tilde (3) is obtained using the new e(+)p and previously published e p neutral current cross section data at high Q(2). These data together with H1 low Q(2) precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.
|
|
| 4. |
- Adloff, C, et al.
(författare)
-
Measurement of inclusive jet cross-sections in deep-inelastic ep scattering at HERA
- 2002
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 542:3-4, s. 193-206
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of inclusive jet cross-sections in deep-inelastic ep scattering at HERA is presented based on data with an integrated luminosity of 21.1 pb(-1). The measurement is performed for photon virtualities Q(2) between 5 and 100 GeV2, differentially in Q(2), in the jet transverse energy E-T, in E-T(2)/Q(2) and in the pseudorapidity eta(lab). With the renormalization scale mu(R) = E-T, perturbative QCD calculations in next-to-leading order (NLO) give a good description of the data in most of the phase space. Significant discrepancies are observed only for jets in the proton beam direction with ET below 20 GeV and Q2 below 20 GeV2. This corresponds to the region in which NLO corrections are largest and further improvement of the calculations is thus of particular interest.
|
|
| 5. |
- Adloff, C, et al.
(författare)
-
Measurement of inclusive jet cross sections in photoproduction at HERA
- 2003
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 29:4, s. 497-513
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of e(+)p --> e(+) + jet + X events in the kinematic range of photon virtualities Q(2) less than or equal to 1GeV(2) and photon-proton centre-of-mass energies 95 less than or equal to W-gammap less than or equal to 285GeV represents an integrated luminosity of 24.1pb(-1). Jets are defined using the inclusive k(perpendicular to) algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy E-T(jet) and pseudorapidity eta(jet) in the domain 5 less than or equal to E-T(jet) less than or equal to 75GeV and -1 less than or equal to eta(jet) less than or equal to 2.5. The cross sections are found to be in good agreement with next-to-leading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in E-T(jet), which varies by six orders of magnitude over the measured range, is compared with similar distributions from p (p) over bar colliders at equal and higher energies.
|
|
| 6. |
- Adloff, C, et al.
(författare)
-
Search for excited electrons at HERA
- 2002
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 548:1-2, s. 35-44
-
Tidskriftsartikel (refereegranskat)abstract
- A search for excited electron (e*) production is described in which the electroweak decays e* --> egamma, e* --> eZ and e* ---> nuW are considered. The data used correspond to an integrated luminosity of 120 pb(-1) taken in e(+/-)p collisions from 1994 to 2000 with the H1 detector at HERA at centre-of-mass energies of 300 and 318 GeV. No evidence for a signal is found. Mass dependent exclusion limits are derived for the ratio of the couplings to the compositeness scale, f/A. These limits extend the excluded region to higher masses than has been possible in previous direct searches for excited electrons. (C) 2002 Published by Elsevier Science B.V.
|
|
| 7. |
- Adloff, C, et al.
(författare)
-
Search for new physics in e +/- q contact interactions at HERA
- 2003
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 568:1-2, s. 35-47
-
Tidskriftsartikel (refereegranskat)abstract
- Deep-inelastic e(+/-) p scattering at high squared momentum transfer Q(2) up to 30 000 GeV2 is used to search for eq contact interactions associated to scales far beyond the HERA centre of mass energy. The neutral current cross section measurements dsigma / dQ(2), corresponding to integrated luminosities of 16.4 pb(-1) of e(-) p data and 100.8 pb(-1) of e(+) p data, are well described by the Standard Model and are analysed to set constraints on new phenomena. For conventional contact interactions lower limits are set on compositeness scales A ranging between 1.6-5.5 TeV. Couplings and masses of leptoquarks and squarks in R-parity violating supersymmetry are constrained to M / lambda > 0.3-1.4 TeV. A search for low scale quantum gravity effects in models with large extra dimensions provides limits on the effective Planck scale of MS > 0.8 TeV. A form factor analysis yields a bound on the radius of light quarks of R-q < 1.0 10(-18) m. (C) 2003 Published by Elsevier B.V.
|
|
| 8. |
- Andreev, V, et al.
(författare)
-
Isolated electrons and muons in events with missing transverse momentum at HERA
- 2003
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 561:3-4, s. 241-257
-
Tidskriftsartikel (refereegranskat)abstract
- A search for events with a high-energy isolated electron or muon and missing transverse momentum has been performed at the electron-proton collider HERA using an integrated luminosity of 13.6 pb(-1) in e(-) p scattering and 104.7 pb(-1) in e(+) p scattering. Within the Standard Model such events are expected to be mainly due to W boson production with subsequent leptonic decay. In e(-) p interactions one event is observed in the electron channel and none in the muon channel, consistent with the expectation of the Standard Model. In the e(+) p data a total of 18 events are seen in the electron and muon channels compared to an expectation of 12.4 +/- 1.7 dominated by W production (9.4 +/- 1.6). Whilst the overall observed number of events is broadly in agreement with the number predicted by the Standard Model, there is-an excess of events with transverse momentum of the hadronic system greater than 25 GeV with 10 events found compared to 2.9 +/- 0.5 expected. The results are used to determine the cross-section for events with an isolated electron or muon and missing transverse momentum. (C) 2003 Published by Elsevier Science B.V.
|
|
| 9. |
- Aktas, A, et al.
(författare)
-
Diffractive photoproduction of J/psi mesons with large momentum transfer at HERA
- 2003
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 568:3-4, s. 205-218
-
Tidskriftsartikel (refereegranskat)abstract
- The diffractive photoproduction of J/psi mesons is measured with the HI detector at the ep collider HERA using an integrated luminosity of 78 pb(-1). The differential cross section dsigma(gammap --> J/psiY)/dt is studied in the range 2 < < 30 GeV2, where t is the square of the four-momentum transferred at the proton vertex. The cross section is also presented as a function of the photon-proton centre-of-mass energy W-gammap in three t intervals, spanning the range 50 < W-gammap < 200 GeV. A fast rise of the cross section with W-gammap is observed for each t range and the slope for the effective linear Pomeron trajectory is measured to be alpha' = -0.0135 +/- 0.0074(stat.) +/- 0.0051(syst.) GeV-2. The measurements are compared with perturbative QCD models based on BFKL and DGLAP evolution. The data are found to be compatible with s-channel helicity conservation. (C) 200 Published by Elsevier B.V.
|
|
| 10. |
- Aktas, A, et al.
(författare)
-
Evidence for a narrow anti-charmed baryon state
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 588:1-2, s. 17-28
-
Tidskriftsartikel (refereegranskat)abstract
- A narrow resonance in D*(-)p and D*(+)(p) over bar invariant mass combinations is observed in inelastic electron-proton collisions at centre-of-mass energies of 300 GeV and 320 GeV at HERA. The resonance has a mass of 3099 +/- 3(stat.) +/- 5(syst.) MeV and a measured Gaussian width of 12 +/- 3(stat.) MeV, compatible with the experimental resolution. The resonance is interpreted as an anti-charmed baryon with a minimal constituent quark composition of uudd (c) over bar, together with the charge conjugate. (C) 2004 Elsevier B.V. All rights reserved.
|
|
| 11. |
- Aktas, A, et al.
(författare)
-
Inclusive dijet production at low Bjorken-x in deep inelastic scattering
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:4, s. 477-493
-
Tidskriftsartikel (refereegranskat)abstract
- Dijet production in deep inelastic ep scattering is investigated in the region of low values of the Bjorken-variable x (10(-4) < x < 10(-2)) and low photon virtualities Q(2) (5 < Q(2) < 100 GeV2). The measured dijet cross sections are compared with perturbative QCD calculations in next-to-leading order. For most dijet variables studied, these calculations can provide a reasonable description of the data over the full phase space region covered, including the region of very low x. However, large discrepancies at low x and low Q(2) are observed for events with small separation in azimuth between the two highest transverse momentum jets. This region of phase space is described better by predictions based on the CCFM evolution equation, which incorporates k(t) factorized unintegrated parton distributions. A reasonable description can be also obtained using the Color Dipole Model or models incorporating virtual photon structure.
|
|
| 12. |
- Aktas, A, et al.
(författare)
-
Measurement of anti-deuteron photoproduction and a search for heavy stable charged particles at HERA
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 36:4, s. 413-423
-
Tidskriftsartikel (refereegranskat)abstract
- The cross section for anti-deuteron photoproduction is measured at HERA at a mean centre-of-mass energy of W-gammap=200 GeV in the range 0.2 < p(T)/M < 0.7 and y < 0.4, where M, p(T) and y are the mass, transverse momentum and rapidity of the anti-deuteron in the HERA laboratory frame, respectively. The numbers of anti-deuterons per event are found to be similar in photoproduction to those in central proton-proton collisions at the CERN ISR but much lower than those in central Au-Au collisions at RHIC. The coalescence parameter B-2, which characterizes the likelihood of anti-deuteron production, is measured in photoproduction to be 0.010+/-0.002+/-0.001, which is much higher than in Au-Au collisions at a similar nucleon-nucleon centre-of-mass energy. No significant production of particles heavier than deuterons is observed and upper limits are set on the photoproduction cross sections for such particles.
|
|
| 13. |
- Aktas, A, et al.
(författare)
-
Measurement of dijet production at low Q(2) at HERA
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 37:2, s. 141-159
-
Tidskriftsartikel (refereegranskat)abstract
- Triple differential dijet cross sections in e(+/-)p interactions are presented in the region of photon virtualities 2 < Q(2) < 80 GeV2, inelasticities 0.1 < y < 0.85, jet transverse energies E*(T1) > 7GeV, E*(T2) > 5 GeV, and pseudorapidities - 2.5 < η(1)*, η(2)* < 0. The measurements are made in the gamma*p centre-of-mass frame, using an integrated luminosity of 57 pb(-1). The data are compared with NLO QCD calculations and LO Monte Carlo programs with and without a resolved virtual photon contribution. NLO QCD calculations fail to describe the region of low Q(2) and low jet transverse energies, in contrast to a LO Monte Carlo generator which includes direct and resolved photon interactions with both transversely and longitudinally polarised photons. Initial and final state parton showers are tested as a mechanism for including higher order QCD effects in low E-T jet production.
|
|
| 14. |
- Aktas, A, et al.
(författare)
-
Measurement of the proton structure function F-2 at low Q(2) in QED Compton scattering at HERA
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 598:3-4, s. 159-171
-
Tidskriftsartikel (refereegranskat)abstract
- The proton structure function F-2(x, Q(2)) is measured in inelastic QED Compton scattering using data collected with the H1 detector at HERA. QED Compton events are used to access the kinematic range of very low virtualities of the exchanged photon, Q(2), down to 0.5 GeV2, and Bjorken x up to similar to 0.06, a region which has not been covered previously by inclusive measurements at HERA. The results are in agreement with the measurements from fixed target lepton-nucleon scattering experiments. (C) 2004 Published by Elsevier B.V.
|
|
| 15. |
- Aktas, A, et al.
(författare)
-
Multi-electron production at high transverse momenta in ep collisions at HERA
- 2003
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 31:1, s. 17-29
-
Tidskriftsartikel (refereegranskat)abstract
- Multi-electron production is studied at high electron transverse momentum in positron- and electron-proton collisions using the H1 detector at HERA. The data correspond to an integrated luminosity of 115 pb(-1). Di-electron and tri-electron event yields are measured. Cross sections are derived in a restricted phase space region dominated by photon-photon collisions. In general good agreement is found with the Standard Model predictions. However, for electron pair invariant masses above 100 GeV, three di-electron events and three tri-electron events are observed, compared to Standard Model expectations of 0.30 +/- 0.04 and 0.23 +/- 0.04, respectively.
|
|
| 16. |
- Aktas, A, et al.
(författare)
-
Search for single top quark production in ep collisions at HERA
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:1, s. 9-22
-
Tidskriftsartikel (refereegranskat)abstract
- A search for single top quark production is performed in e(+/-) pcollisions at HERA. The search exploits data corresponding to an integrated luminosity of 118.3 pb(-1). A model for the anomalous production of top quarks in a flavour changing neutral current process involving a tugamma coupling is investigated. Decays of top quarks into a b quark and a W boson are considered in the leptonic and the hadronic decay channels of the W. Both a cut-based analysis and a multivariate likelihood analysis are performed to discriminate anomalous top quark production from Standard Model background processes. In the leptonic channel, 5 events are found while 1.31 +/- 0.22 events are expected from the Standard Model background. In the hadronic channel, no excess above the expectation for Standard Model processes is found. These observations lead to a cross section (ep --> e t X) = 0.29(-0.14)(+0.15) pb at roots = 319 GeV. Alternatively, assuming that the observed events are due to a statistical fluctuation, upper limits of 0.55 pb on the anomalous top production cross section and of 0.27 on the tugamma coupling k(tugamma) are established at the 95% confidence level.
|
|
| 17. |
- Aktas, A, et al.
(författare)
-
Search for squark production in R-parity violating supersymmetry at HERA
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 36:4, s. 425-440
-
Tidskriftsartikel (refereegranskat)abstract
- A search for squarks in R-parity violating supersymmetry is performed in e(+/-)p collisions at HERA using the H1 detector. The data were taken at a centre-of-mass energy of 319 GeV and correspond to an integrated luminosity of 64.3 pb(-1) for e (+) p collisions and 13.5 pb(-1) for e(-)p collisions. The resonant production of squarks via a Yukawa coupling lambda' is considered, taking into account direct and indirect R-parity violating decay modes. No evidence for squark production is found in the multi-lepton and multi-jet final state topologies investigated. Mass dependent limits on lambda' are obtained in the framework of the Minimal Supersymmetric Standard Model. In addition, the results are interpreted in terms of constraints on the parameters of the minimal Supergravity model. At the 95% confidence level squarks of all flavours with masses up to 275 GeV are excluded in a large part of the parameter space for a Yukawa coupling of electromagnetic strength. For a coupling strength 100 times smaller, masses up to 220 GeV can be ruled out.
|
|
| 18. |
- Aktas, A, et al.
(författare)
-
A general search for new phenomena in ep scattering at HERA
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 602:1-2, s. 14-30
-
Tidskriftsartikel (refereegranskat)abstract
- A model-independent search for deviations from the Standard Model prediction is performed in e(+) p and e(-) p collisions at HERA using H1 data corresponding to an integrated luminosity of 117 pb(-1). For the first time all event topologies involving isolated electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A statistical algorithm is developed to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or invariant mass of final state particles and to quantify their significance. A good agreement with the Standard Model prediction is observed in most of the event classes. The most significant deviation is found for a topology containing an isolated muon, missing transverse momentum and a jet, consistent with a previously reported observation.
|
|
| 19. |
- Aktas, A, et al.
(författare)
-
Muon pair production in ep collisions at HERA
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 583:1-2, s. 28-40
-
Tidskriftsartikel (refereegranskat)abstract
- Cross sections for the production of two isolated muons up to high di-muon masses are measured in ep collisions at HERA with the H1 detector in a data sample corresponding to an integrated luminosity of 71 pb(-1) at a centre of mass energy of roots = 319 GeV. The results are in good agreement with Standard Model predictions, the dominant process being photon-photon interactions. Additional muons or electrons are searched for in events with two high transverse momentum muons using the full data sample corresponding to 114 pb(-1), where data at roots = 301 GeV and roots = 319 GeV are combined. Both the di-lepton sample and the tri-lepton sample agree Well with the predictions. (C) 2004 Published by Elsevier B.V.
|
|
| 20. |
- Aktas, A, et al.
(författare)
-
Search for bosonic stop decays in R-parity violating supersymmetry in e(+)p collisions at HERA
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 599:3-4, s. 159-172
-
Tidskriftsartikel (refereegranskat)abstract
- A search for scalar top quarks in R-parity violating supersymmetry is performed in e(+)p collisions at HERA using the H1 detector. The data, taken at roots = 319 GeV and 301 GeV, correspond to an integrated luminosity of 106 pb(-1). The resonant production of scalar top quarks t in positron quark fusion via an R-parity violating Yukawa coupling lambda' is considered with the subsequent bosonic stop decay t --> BW. The R-parity violating decay of the sbottom quark b --> dv(e) and leptonic and hadronic W decays are considered. No evidence for stop production is found in the search for bosonic stop decays nor in a search for the direct R-parity violating decay t --> eq. Mass dependent limits on lambda' are obtained in the framework of the minimal supersymmetric Standard Model. Stop quarks with masses up to 275 GeV can be excluded at the 95% confidence level for a Yukawa coupling of electromagnetic strength. (C) 2004 Elsevier B.V. All rights reserved.
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
- Laptev, Ivan, et al.
(författare)
-
Automatic extraction of roads from aerial images based on scale space and snakes
- 2000
-
Ingår i: Machine Vision and Applications. - : Springer. - 0932-8092 .- 1432-1769. ; 12:1, s. 23-31
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a new approach for automatic road extraction from aerial imagery with a model and a strategy mainly based on the multi-scale detection of roads in combination with geometry-constrained edge extraction using snakes. A main advantage of our approach is, that it allows for the first time a bridging of shadows and partially occluded areas using the heavily disturbed evidence in the image. Additionally, it has only few parameters to be adjusted. The road network is constructed after extracting crossings with varying shape and topology. We show the feasibility of the approach not only by presenting reasonable results but also by evaluating them quantitatively based on ground truth.
|
|
| 24. |
- Sciandra, Francesca, et al.
(författare)
-
Identification of the beta-dystroglycan binding epitope within the C-terminal region of alpha-dystroglycan
- 2001
-
Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956. ; 268:16, s. 4590-4597
-
Tidskriftsartikel (refereegranskat)abstract
- Dystroglycan is a receptor for extracellular matrix proteins that plays a crucial role during embryogenesis in addition to adult tissue stabilization. A precursor product of a single gene is post-translationally cleaved to form two different subunits, alpha and beta. The extracellular alpha-dystroglycan is a membrane-associated, highly glycosylated protein that binds to various extracellular matrix molecules, whereas the transmembrane beta-dystroglycan binds, via its cytosolic domain, to dystrophin and many other proteins. alpha- and beta-Dystroglycan interact tightly but noncovalently. We have previously shown that the N-terminal region of beta-dystroglycan, beta-DG(654-750), binds to the C-terminal region of murine alpha-dystroglycan independently from glycosylation. Preparing a series of deleted recombinant fragments and using solid-phase binding assays, the C-terminal sequence of alpha-dystroglycan containing the binding epitope for beta-dystroglycan has been defined more precisely. We found that a region of 36 amino acids, from position 550-585, is required for binding the extracellular region, amino acids 654-750 of beta-dystroglycan. Recently, a dystroglycan-like gene was identified in Drosophila that showed a moderate degree of conservation with vertebrate dystroglycan (31% identity, 48% similarity). Surprisingly, the Drosophila sequence contains a region showing a higher degree of identity and conservation (45% and 66%) that coincides with the 550-585 sequence of vertebrate alpha-dystroglycan. We have expressed this Drosophila dystroglycan fragment and measured its binding to the extracellular region of vertebrate (murine) beta-dystroglycan (Kd = 6 +/- 1 microM). These data confirm the proper identification of the beta-dystroglycan binding epitope and stress the importance of this region during evolution. This finding might help the rational design of dystroglycan-specific binding drugs, that could have important biomedical applications.
|
|
