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Biomedical subjects

E R Johnston

Publications and source records attributed to E R Johnston.

6 recordsLinked to original sources
PubMed2000

The SU and TM envelope protein subunits of bovine leukemia virus are linked by disulfide bonds, both in cells and in virions.

After the polyprotein precursor of retroviral envelope proteins is proteolytically cleaved, the surface (SU) and transmembrane (TM) subunits remain associated with each other by noncovalent interactions or by disulfide bonds. Disulfide linkages confer a relatively stable association between the SU and TM envelope protein subunits of Rous sarcoma virus and murine leukemia virus. In contrast, the noncovalent association between SU and TM of human immunodeficiency virus leads to significant shedding of SU from the surface of infected cells. The SU and TM proteins of bovine leukemia virus (BLV) initially were reported to be disulfide linked but later were concluded not to be, since TM is often lost during purification of SU protein. Here, we show that SU and TM of BLV do, indeed, associate through disulfide bonds, whether the envelope proteins are overexpressed in transfected cells, are produced in virus-infected cells, or are present in newly produced virions.

Animals↗
PubMed1996

Peripheral blood mononuclear cells from sheep infected with a variant of bovine leukemia virus synthesize envelope glycoproteins but fail to induce syncytia in culture.

Peripheral blood mononuclear cells (PBMCs) infected with the oncogenic retrovirus bovine leukemia virus (BLV) produce virus when cultured briefly. BLV can be transmitted in cocultures to adherent susceptible cells, which become infected, express viral proteins, and fuse into multinucleated syncytia several days later. PBMCs from 3 of 10 BLV-infected sheep displayed a lifelong deficiency in induction of syncytium formation among indicator cells in culture, although large numbers of PBMCs synthesized viral transcripts or capsid protein. Since the infected, syncytium-deficient PBMCs were > or = 97% B cells, the deficiency could not be attributed to altered host cell tropism. The syncytium-deficient phenotype was recapitulated in newly infected sheep, demonstrating that this property is regulated by the viral genotype. The alteration in the BLV genome delayed but did not prohibit the establishment of BLV infection in vivo. Envelope glycoproteins were synthesized in syncytium-deficient PBMCs, translocated to the cell surface, and incorporated into virions. However, monoclonal antibodies specific for the BLV surface glycoprotein did not stain fixed PBMCs of the syncytium-deficient phenotype. Moreover, an animal with syncytium-deficient PBMCs had lower titers of neutralizing antibodies throughout the first 5 years of infection than an animal with similar numbers of infected PBMCs of the syncytium-inducing phenotype. The syncytium-deficient variant productively infected indicator cells at greatly reduced efficiency, showing that the alteration affects an early step in viral entry or replication. These results suggest that the alteration maps in the env gene or in a gene whose product affects the maturation or conformation, and consequently the function, of the envelope protein complex.

Animals↗
PubMed1996

Dynamic response of electromagnetic spatial displacement trackers.

Overall system latency--the elapsed time from input human motion until the immediate consequences of that input are available in the display--is one of the most frequently cited shortcoming of current virtual environment (VE) technology. Given that spatial displacement trackers are employed to monitor head and hand position and orientation in many VE applications, the dynamic response intrinsic to these devices is an unavoidable contributor to overall system latency. In this paper, we describe a testbed and method for measurement of tracker dynamic response that use a motorized rotary swing arm to sinusoidally displace the VE sensor at a number of frequencies spanning the bandwidth of volitional human movement. During the tests, actual swing arm angle and VE sensor reports are collected and time stamped. By calibrating the time stamping technique, the tracker's internal transduction and processing time are separated from data transfer and host computer software execution latencies. We have used this test-bed to examine several VE sensors--most recently to compare latency, gain, and noise characteristics of two commercially available electromagnetic trackers: Ascension Technology Corp.'s Flock of Birds(TM) and Polhemus Inc.'s Fastrak(TM).

Computer Systems↗
PubMed1993

The solution conformation of (D)Phe-Pro-containing peptides: implications on the activity of Ac-(D)Phe-Pro-boroArg-OH, a potent thrombin inhibitor.

Ac-(D)Phe-Pro-boroArg-OH is a potent, competitive inhibitor of thrombin (Ki = 40 pM). 1H-NMR studies have shown that the peptide portion, -(D)Phe-Pro-, has secondary structure in aqueous solutions. This structure corresponds fairly closely to the structure of H-(D)Phe-Pro-ArgCH2Cl complexed to thrombin in the protein crystal structure (Bode, W.; et al. EMBO J. 1989, 193, 3467-3475.). These results indicate that, in addition to enthalpic interactions in the active site of the enzyme, there are significant entropic advantages in binding this molecule not previously recognized. We estimate that they contribute approximately 10-fold to binding. The structure we have observed can be explained by pi-pi interactions between the phenyl side chain of (D)Phe and the (D)Phe-Pro peptide bond. Assignment of structure is based first on the 0.8-1.2 ppm difference between the two Pro C delta protons. The magnitude of these chemical shifts are consistent with aromatic ring current-induced effects expected for distances in our structure. The structure was further defined by interproton distances and correlation times calculated by backtransformation and correction of the NOESY and ROESY data to the longitudinal and transverse cross relaxation rates. Analysis of the vicinal coupling constants show that Phe chi 1 is not fixed. Correlation times for the peptide side chains and backbone indicate that the phenyl ring and boroArg side chain possess various degrees of internal motion, and that the rest of the peptide has a fairly rigid conformation.

Boron Compounds↗
PubMed1990

A survey of optometric practice in New York State: trends and policy considerations.

A mail survey of actively practicing optometrists in New York state revealed information about present and future manpower supply, modes of practice, procedures and instrumentation used, services rendered, third party reimbursement and involvement in continuing education. The survey illustrates the need to increase the gathering of such data in order to analyze practice patterns and more accurately initiate short- and long-term planning within the profession.

Adult↗