Showing papers by "Robert McKenna published in 1998"

Structure determination of the phiX174 closed procapsid.

Abstract: The structure of a procapsid of the single-stranded DNA bacteriophage ++phiX174 was determined to 3.5 A resolution. The crystal space group was I213 with a unit-cell length of 774 A. The unit cell contained 16 icosahedral virus particles, each situated on a crystallographic threefold axis. Thus, there are two independent one-thirds of a particle per asymmetric unit, and a total of 40-fold non-crystallographic redundancy. To aid in the interpretation of the packing arrangement, crystals were prepared for thin sectioning and analyzed by electron microscopy. Oscillation X-ray diffraction data was collected on image plates using synchrotron radiation and oscillation angles of either 0.25 or 0.30 degrees. A low-resolution 6.5 A data set collected from a single frozen crystal was particularly helpful in the structure determination, because of its completeness and internal consistency. The initial particle orientations were determined using self-rotation functions, while the initial position of one particle was determined from a Patterson map. The structure was solved by molecular replacement real-space averaging using a model based on a cryo-electron microscopy reconstruction as a starting point for the phase determination. The initial structure determination used the data between 20 and 13 A resolution, which was then extended one reciprocal lattice point at a time to 6.5 A resolution. At this point, a 3.5 A resolution data set compiled from a number of crystals collected at 277 K was introduced. Phase extension and averaging continued to 3.5 A resolution after re-determining the particle positions and orientations. The amino-acid sequences of most of the D, F and G proteins and part of the B protein could be unambiguously built into the 3.5 A electron-density map. Partial crystallographic refinement yielded an R factor of 31.6%, consistent with the relatively low resolution and lack of completeness of the data.

An Animal Model for Lung Volume Reduction Therapy of Pulmonary Emphysema

Abstract: Stapled lung volume reduction surgery (LVRS) has recently been described for treatment of emphysema. Many questions arise regarding physiologic mechanisms of response from surgical treatment of emphysema. The objective of this study was to develop an animal model for the study of lung volume reduction surgery in diffuse heterogeneous emphysema. We hypothesized that elastic recoil would increase, static respiratory system compliance would decrease, and expiratory flows would increase after lung volume reduction surgery in animals with emphysema. In the study, emphysema was induced in 31 New Zealand White rabbits (3-5 kg) with endotracheally aerosalized porcine elastase (10,000-12,000 U). Lateral thoracotomies were performed 4-6 weeks postinduction under general anesthesia and mechanical ventilatory support. Stapled volume reduction was performed on the right lower lobe using a standard multirow pediatric stapler (U.S. Surgical). Pulmonary function tests were performed at baseline (preinduction), before stapling LVRS (postemphysema induction), immediately post stapling LVRS, and 1 week poststapling. Static respiratory system compliance, flow, conductance and forced expiratory flows, and peak flows at 20 and 40 cm3 of exhaled volume were analyzed. Animals were sacrificed 1 week poststapling, and bilateral lungs were harvested for histopathology. Diffuse but heterogeneous pulmonary emphysema was seen in these animals treated with high-dose aerosolized elastase. Static compliance increased, while expiratory flows and conductance decreased after induction of emphysema. Immediately post stapled volume reduction therapy, animals had decreased static compliance. By 1 week following surgery, animals showed increased forced expiratory flows and decreased expiratory resistance, although compliance was similar to preoperative levels. In conclusion, we describe initial results in an animal model of obstructive emphysema suitable for the study of lung volume reduction surgery. Changes in pulmonary function indicate that unilateral lower lobe LVRS increases airway conductance in the rabbits. Findings from LVRS studies in animal models such as this may help explain clinical improvement following LVRS in humans.

Use of Non-Crystallographic Symmetry for Ab Initio Phasing of Virus Structures

Abstract: Several virus structures have now been determined through ab initio phasing at very low (~20A) resolution followed by extension to high resolution using their non-crystallographic symmetry (NCS). The methods are described, and post-mortem investigations of phase determination are analyzed, particularly for relevance to the more challenging general case of ab initio determination of protein structure.