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Biomedical subjects

G Briscoe

Publications and source records attributed to G Briscoe.

11 recordsLinked to original sources
PubMed2000

Defining fibronectin's cell adhesion synergy site by site-directed mutagenesis.

Fibronectin's RGD-mediated binding to the alpha5beta1 integrin is dramatically enhanced by a synergy site within fibronectin III domain 9 (FN9). Guided by the crystal structure of the cell-binding domain, we selected amino acids in FN9 that project in the same direction as the RGD, presumably toward the integrin, and mutated them to alanine. R1379 in the peptide PHSRN, and the nearby R1374 have been shown previously to be important for alpha5beta1-mediated adhesion (Aota, S., M. Nomizu, and K.M. Yamada. 1994. J. Biol. Chem. 269:24756-24761). Our more extensive set of mutants showed that R1379 is the key residue in the synergistic effect, but other residues contribute substantially. R1374A decreased adhesion slightly by itself, but the double mutant R1374A-R1379A was significantly less adhesive than R1379A alone. Single mutations of R1369A, R1371A, T1385A, and N1386A had negligible effects on cell adhesion, but combining these substitutions either with R1379A or each other gave a more dramatic reduction of cell adhesion. The triple mutant R1374A/P1376A/R1379A had no detectable adhesion activity. We conclude that, in addition to the R of the PHRSN peptide, other residues on the same face of FN9 are required for the full synergistic effect. The integrin-binding synergy site is a much more extensive surface than the small linear peptide sequence.

Amino Acid Sequence↗
PubMed2000

Vision as temporal trace.

Most current models of human and animal vision assume that the processes of vision involve 2D (or even 3D) internal representations of the external world--an iconic representation. Within these models, recognition involves some form of lineal, areal or volumetric comparison of these internal representations (either learned or innate) with current sensory inputs. However, this view has recently come under criticism. In this paper, a neural model of vision is explored in which this iconic world view is replaced by a temporally ordered trace of (essentially) local features. The model employs hierarchical, recurrently linked, self-organizing topological maps.

Animals↗
PubMed1999

The compact conformation of fibronectin is determined by intramolecular ionic interactions.

Fibronectin exists in a compact or extended conformation, depending upon environmental pH and salt concentration. Using recombinant fragments expressed in bacteria and baculovirus, we determined the domains responsible for producing fibronectin's compact conformation. Our velocity and equilibrium sedimentation data show that FN2-14 (a protein containing FN-III domains 2 through 14) forms dimers in low salt. Experiments with smaller fragments indicates that the compact conformation is produced by binding of FN12-14 of one subunit to FN2-3 of the other subunit in the dimer. The binding is weakened at higher salt concentrations, implying an electrostatic interaction. Furthermore, segment FN7-14+A, which contains the alternatively spliced A domain between FN11 and 12, forms dimers, whereas FN7-14 without A does not. Segment FN12-14+A also forms dimers, but the isolated A domain does not. These data imply an association of domain A with FN12-14, and the presence of A may favor an open conformation by competing with FN2-3 for binding to FN12-14.

Animals↗
PubMed1998

The symmetrical structure of structural maintenance of chromosomes (SMC) and MukB proteins: long, antiparallel coiled coils, folded at a flexible hinge.

Structural maintenance of chromosomes (SMC) proteins function in chromosome condensation and several other aspects of DNA processing. They are large proteins characterized by an NH2-terminal nucleotide triphosphate (NTP)-binding domain, two long segments of coiled coil separated by a hinge, and a COOH-terminal domain. Here, we have visualized by EM the SMC protein from Bacillus subtilis (BsSMC) and MukB from Escherichia coli, which we argue is a divergent SMC protein. Both BsSMC and MukB show two thin rods with globular domains at the ends emerging from the hinge. The hinge appears to be quite flexible: the arms can open up to 180 degrees, separating the terminal domains by 100 nm, or close to near 0 degrees, bringing the terminal globular domains together. A surprising observation is that the approximately 300-amino acid-long coiled coils are in an antiparallel arrangement. Known coiled coils are almost all parallel, and the longest antiparallel coiled coils known previously are 35-45 amino acids long. This antiparallel arrangement produces a symmetrical molecule with both an NH2- and a COOH-terminal domain at each end. The SMC molecule therefore has two complete and identical functional domains at the ends of the long arms. The bifunctional symmetry and a possible scissoring action at the hinge should provide unique biomechanical properties to the SMC proteins.

Bacterial Proteins↗
PubMed1998

CQI teamwork: reevaluate, restructure, renew.

Here, a continuous quality improvement (CQI) team evaluates and streamlines hospital processes, and impacts admission and transportation, medication administration, and morale.

Hospital Restructuring↗
PubMed1993

The use of midazolam for hypnosedative interviews.

The authors describe three cases in which midazolam was successfully used in diagnostic hypnosedative interviews. A discussion comparing and contrasting midazolam to other intravenous hypnosedatives is presented. The authors suggest that midazolam is an effective agent for diagnostic hypnosedative interviews and may be preferable to other agents when posthypnotic recollection of interview content is undesirable.

Adult↗
PubMed1990

Purification of hexabrachion (tenascin) from cell culture conditioned medium, and separation from a cell adhesion factor.

We describe a protocol for purifying hexabrachion from conditioned medium of cell cultures, using gel filtration chromatography on Sephacryl 500, followed by anion-exchange chromatography on a Mono Q column, followed optionally by a second gel filtration or zone sedimentation on glycerol gradients. The protocol has several advantages over previous procedures based on affinity chromatography on monoclonal antibodies. Perhaps foremost, the protein is never exposed to the denaturing solvents that are required for elution from the antibody column. The Mono Q column also separated hexabrachion from a prominent cell adhesion activity that eluted with the hexabrachion on the first gel filtration, and co-sedimented with hexabrachions on glycerol gradients. The cell adhesion fractions showed several bands between 190 and 400 kDa. A single band at 220 kDa stained prominently with a polyclonal antibody against mouse EHS laminin, and a band at 190 kDa stained with a monoclonal antibody against s-laminin. The purification protocol gave hexabrachion at high concentration and with no detectable contamination by fibronectin or laminin. The highest yield of hexabrachion (1-4 mg from 400 ml of conditioned medium) was from human glioblastoma cell cultures, but the same procedure allowed us to purify and characterize the rat hexabrachion. Protein purified from primary cultures of rat embryo fibroblasts showed approximately equal amounts of three subunit sizes: 280, 230, and 220 kDa. These different subunits, presumably derived from alternative RNA splicing, appeared to be segregated into large and small hexabrachions, which could be separated on glycerol gradients.

Astrocytes↗
PubMed1989

Biochemical and structural studies of tenascin/hexabrachion proteins.

Tenascin is a large, disulfide-bonded glycoprotein of the extracellular matrix. The predominant form of tenascin observed by electron microscopy is a six-armed oligomer, termed a hexabrachion. We have determined the molecular mass of the native human hexabrachion to be 1.9 x 10(6) Da by sedimentation equilibrium analysis and by electrophoresis on non-reducing agarose gels. On reducing polyacrylamide gel electrophoresis (SDS-PAGE), human tenascin showed a single prominent band at 320 kDa and minor bands of 220 and 230 kDa. The molecular weight of the native human hexabrachion is thus consistent with a disulfide-bonded hexamer of the 320 kDa subunits. Upon treatment with neuraminidase, the apparent molecular weights of all human and chicken tenascin subunits on reducing SDS-PAGE were decreased by about 10 kDa. Prolonged incubation with alpha-mannosidase, however, caused no apparent change in the apparent molecular weight of tenascin subunits. Sedimentation in a cesium chloride gradient gave a higher buoyant density for human tenascin than for fibronectin, suggesting that it has a higher degree of glycosylation. The far-UV circular dichroism spectrum indicates a predominance of beta-structure and a lack of collagen-like or alpha-helical structure. When human hexabrachions were reduced and acetylated, the resulting fragments were single arms which sedimented at 6 S in glycerol gradients and migrated at 320 kDa on non-reducing gels. Treatment of tenascin with trypsin and alpha-chymotrypsin also produced large fragments which were fractionated by gradient sedimentation and analyzed by non-reducing SDS-PAGE and electron microscopy. We present a structural model for the assembly of the observed fragments into the elaborate native hexabrachion.

Animals↗
PubMed1987

Calcified renal masses.

A review of the literature and the University of Kentucky Medical Center/Lexington Veterans Administration Medical Center experience regarding calcification of renal masses was undertaken. Twenty per cent of calcified renal masses cannot be easily characterized by CT scan as malignant or benign and are indeterminate. These lesions must be followed closely with follow-up CT scanning or undergo surgical exploration, as 40 per cent may be malignant.

Calcinosis↗
PubMed1983

Target recovery in visual backward masking: no clear explanation in sight.

Theories of visual backward masking have generally ignored demonstrations of the perceptual recovery of a masked target when the masking stimulus (M1) is followed by a second masking stimulus (M2). This failure to address recovery may reflect a belief that recovery effects are relatively small and inconsistent. The present article reports a series of experiments, using single-letter targets, a patterned M1 and a light-flash M2, which indicate that recovery can be a robust and substantial phenomenon. It is observable under a variety of conditions, and the magnitude of recovery matches the masking effect itself. A two-choice discrimination task was employed to test an explanation for recovery that attributes the effect to inhibition from the transient response to the light flash on the sustained response to the patterned mask. That explanation calls for the shape of the function relating the discriminability of the patterned mask to the onset asynchrony of M1 and M2 to be U-shaped in form. The data, however, reveal a monotonic masking function, suggesting that only sustained, intrachannel interactions are involved in the recovery of the target percept. Two conflicting explanations for recovery are discussed, one based upon inhibition of M1 responses, the other upon enhancement of target features. Thus, while recovery is demonstrated to be very real, its explanation remains elusive.

Adolescent↗