Applications of DNA shuffling to pharmaceuticals and vaccines

DNA shuffling is a practical process for directed molecular evolution which uses recombination to dramatically accelerate the rate at which one can evolve genes. Single and multigene traits that require many mutations for improved phenotypes can be evolved rapidly. DNA shuffling technology has been significantly enhanced in the past year, extending its range of applications to small molecule pharmaceuticals, pharmaceutical proteins, gene therapy vehicles and transgenes, vaccines and evolved viruses for vaccines, and laboratory animal models.     

Mutations in the Saccharomyces Cerevisiae Type 2a Protein Phosphatase Catalytic Subunit Reveal Roles in Cell Wall Integrity, Actin Cytoskeleton Organization and Mitosis

Temperature-sensitive mutations were generated in the Saccharomyces cerevisiae PPH22 gene that, together with its homologue PPH21, encode the catalytic subunit of type 2A protein phosphatase (PP2A). At the restrictive temperature (37°), cells dependent solely on pph22(ts) alleles for PP2A function displayed a rapid arrest of proliferation. Ts(-) pph22 mutant cells underwent lysis at 37°, showing an accompanying viability loss that was suppressed by inclusion of 1 M sorbitol in the growth medium. Ts(-) pph22 mutant cells also displayed defects in bud morphogenesis and polarization of the cortical actin cytoskeleton at 37°. PP2A is therefore required for maintenance of cell integrity and polarized growth. On transfer from 24° to 37°, Ts(-) pph22 mutant cells accumulated a 2N DNA content indicating a cell cycle block before completion of mitosis. However, during prolonged incubation at 37°, many Ts(-) pph22 mutant cells progressed through an aberrant nuclear division and accumulated multiple nuclei. Ts(-) pph22 mutant cells also accumulated aberrant microtubule structures at 37°, while under semi-permissive conditions they were sensitive to the microtubule-destabilizing agent benomyl, suggesting that PP2A is required for normal microtubule function. Remarkably, the multiple defects of Ts(-) pph22 mutant cells were suppressed by a viable allele (SSD1-v1) of the polymorphic SSD1 gene.     

500 MHz H-NMR studies of bile salt-phosphatidylcholine mixed micelles and vesicles Evidence for differential motional restraint on bile salt and phosphatidylcholine resonances

¹H nuclear magnetic resonance (NMR) spectra at 500 MHz have been obtained for taurocholate/egg phosphatidylcholine mixtures of varying composition. The excellent chemical shift dispersion permits identification of most resonances for each component. This high-resolution character of the NMR spectra is retained until the phosphatidylcholine (PC) mole fraction exceeds 60–70% (the exact limit depends on ionic strength). ¹H linewidths have been monitored as a function of solute composition in order to evaluate trends in local molecular mobility of each component as the distribution of aggregate particles is varied, and to examine the effects of added NaCl in altering micellar size and shape. Although prior light scattering studies (Mazer, N.A., Benedek, G.B. and Carey, M.C. (1980) Biochemistry 19, 601–615) and our own work indicate a 6-fold increase in particle hydrodynamic radius from pure taurocholate micelles to 1 : 1 taurocholate/PC mixtures containing 150 mM NaCl, both lipid components retain substantial motional freedom and exhibit narrow NMR signals in this compositional region. As the solubilization limit for PC is approached (approx. 2:1 PC:taurocholate), differential behavior is observed for the two components: the motion of taurocholate becomes preferentially restricted, while polar portions of the PC remain mobile until large multilayers predominate.     

Sensitivity and adaptation in R7, an ultraviolet photoreceptor,in theDrosophila retina

Summary Receptor deficient mutants and chromatic adaptation were used to isolate the contribution of R7 to the electroretinogram (ERG) ofDrosophila. R7 was found to be a single-peaked ultraviolet (UV) receptor (Fig. 1). Photoconversion of the UV absorbing rhodopsin (R) to its stable 470–495 nm metarhodopsin (M) was shown to elicit a long-lived negative (depolarizing) afterpotential (Fig. 3) while inactivating R7. Photoreconversion ofM toR reactivates R7 (Fig. 2) and repolarizes the ERG (Fig. 3). The intensities of light needed to elicit afterpotentials by photointerconverting R7 photopigment were found to be about 2 log units greater than for R1-6 photopigment (Fig. 4). Vitamin A deprivation decreases R7 (as well as R8) sensitivity by about 2 log units (through decreased photopigment levels) without changing spectral sensitivity shape (Fig. 5). Vitamin A deprivation further eliminates the light-induced inactivation of R7 allowing experiments designed to characterize the in vivo spectral absorption of R7M. R7M was found to have UV and 495 nm maxima (Fig. 6). No polarization sensitivity was detected in the R7 ERG component. The adaptational properties of R7 are similar to the properties previously established for R1-6 but different from the properties of R8.Supported by NSF grants BMS-74-12817 and BNS 76-11921. I thank M. Chapin, R. Greenberg, K. Hu, A. Ivanyshyn, D. Lakin, G. Pransky, D. Sawyer, J. Walker and W. Zitzmann for technical assistance.     

Many variable region genes are utilized in the antibody response of BALB/c mice to the influenza virus A/PR/8/34 hemagglutinin

We have examined how many different H chain variable (VH) and kappa-chain variable (Vk) germ-line genes are used in the antibody response to the influenza virus A/PR/8/34 hemagglutinin (PR8 HA), and have assessed how the expression of individual VH and/or Vk genes contributes to the generation of specificity for the HA. A panel of 51 hybridoma antibodies that recognize two antigenic regions on the HA were compared for the sequence of their Ig H and L chain V regions. The hybridomas were obtained from 28 individual BALB/c mice that had been immunized with PR8 under a variety of primary and secondary response immunization protocols. The degree and pattern of sequence similarity suggests that 29 different VH genes drawn from seven different VH gene families, and 25 different Vk genes drawn from 12 different Vk gene families were used in this panel. Based on current estimates of the total numbers of VH and Vk genes in the mouse, this suggests that between 2.5 and 10% of the entire VH and Vk germ-line repertoires were used by these hybridomas. Despite this extensive diversity, some V genes were repetitively identified among these hybridomas, and were most often expressed in the context of specific VH/Vk combinations. Because antibodies that used identical VH/Vk combinations also usually displayed similar reactivity patterns with a panel of mutant viruses, this indicates that VH/Vk pairing can be important in establishing the specificity of antibodies for the HA.     

Intercellular adhesion molecule-1 (ICAM-1)-dependent and ICAM-1-independent adhesive interactions between polymorphonuclear leukocytes and human airway epithelial cells infected with parainfluenza virus type 2.

Acute respiratory virus infections are often associated with an early influx of neutrophils (PMN) into the airways. Maximal cytoxic injury by PMN depends on tight cell-cell adhesion. Infection of some cell types by respiratory and other viruses has been shown to increase PMN adhesion to these cells by undefined mechanisms. We studied adhesion by human PMN to monolayers of primary (1 degree) human tracheal epithelial cells (TEC) or an immortalized cell line derived from human TEC, 9HTEo-, that had been infected with parainfluenza virus type 2 (PiV2). PMN adhesion to uninfected 1 degree TEC was very low (< 5%), but PMN adhesion to PiV2-infected 1 degree TEC was greatly increased (89 +/- 7%). PMN adhesion to 9HTEo- cells was 47 +/- 6%, but increased, 87 +/- 8%, for PiV2-infected 9HTEo- cells. Surface intercellular adhesion molecule-1 (ICAM-1) expression on 1 degree TEC, as determined by immunofluorescence flow cytometry, was relatively low (23 fluorescence units) but doubled by 24 h after PiV2 infection and tripled by 48 h. The 9HTEo- cells constitutively expressed higher levels of surface ICAM-1 (120 units) which did not increase with PiV2 infection. Treatment of non-PiV2-infected 9HTEo- cells with mAb (R6.5) to ICAM-1 reduced PMN adhesion to these cells from 47 +/- 8 to 23 +/- 5%. Identical mAb treatment of either 1 degree TEC or 9HTEo- cells infected with PiV2 had no significant effect on PMN adhesion. Treatment of the PMN with mAb against CD11a, CD11b, or CD18 markedly reduced PMN adhesion to PiV2-infected 1 degree TEC and 9HTEo- cells. We conclude that PiV2 infection of human TEC causes a marked increase in their adhesive interactions with PMN by inducing increased surface expression of both ICAM-1 and one or more, as yet uncharacterized, non-ICAM-1 adhesion molecules that function as counter-receptors for CD11/CD18 on PMN. These mechanisms of adhesion may play a role in epithelial damage during acute respiratory virus infections.