Search

Nosocomial infections after spinal surgery are relatively uncommon but potentially serious. The goal of diagnostic evaluation is to determine the extent of infection and identify the microorganism involved. Neuroimaging provides accurate information on correct topography, localization and propagation of the infection. Microbiological data are able to give aetiological causes. In this patient with severe, chronic polymicrobial spine infection with epidural abscess and CSF fistula due to multidrug-resistant organisms, the cure was achieved with long-term antimicrobial specific therapy with quinupristin-dalfopristin (50 days) and linezolid (100 days) with mild side effects. This positive result was due to combined medical and surgical treatment.

We report a molecular dynamics simulation study of a zinc-protease--gelatinase A or MMP2--which is a major target for drug design, being involved in tumor metastasis and other degenerative diseases. Two structures have been employed as starting conditions, one based on the crystal of multi-domain proMMP2, the other consisting of the catalytic domain only. The overall fold of the two models is maintained over the 1260 ps trajectory, enabling us to analyze correlations of fluctuations among domains, and to observe the presence of correlations within the catalytic domain in the multi-domain enzyme only, hence due to the presence of hemopexin and fibronectin domains. In the multi-domain protein, two cavities are conserved over the trajectory, one of them pointing to a key region, a crevice surrounding the catalytic zinc. The other one is localized across the three domains of the MMP2 metalloproteinase. These areas are partially covered by the propeptide in the crystal structure of proMMP2. We propose a model of MMP2-collagen interaction that involves both identified cavities and takes into account the inter/intra domain cross-correlations.

Electrostatic interactions in two structures of human interferon gamma (hIFNgamma), corresponding to interferon molecule alone and bound to its receptor, were analyzed on the basis of a continuum dielectric model. It was found that a number of titratable groups, mainly basic, show large pK shifts and remain in their neutral forms at physiologically relevant pH. The fact that these groups are largely common to both structures and that most of them belong to the set of most conserved sites suggests that this is a property inherent to the hIFNgamma molecule rather than an artifact of the crystal packing. His111 was also found deprotonated at neutral pH. It was concluded that receptor recognition involving His111 is driven by aromatic coupling of His111 and Tyr52 from the receptor rather than by electrostatic interactions. The structure corresponding to hIFNgamma in complex with its receptor shows a reduction in number and in degree of desolvation of the buried titratable sites. This finding suggested that on receptor binding, hIFNgamma adopts energetically more favorable, relaxed, conformation. It was experimentally shown that in contrast to the full-size hIFNgamma, the construct having 21 amino acid residues deleted from the C-terminus is soluble. The hydrophobicity profile analysis suggested that factors other than the exposure of hydrophobic parts of the molecule are responsible for the low stability and propensity for aggregation. On the basis of these results, it was assumed that the electrostatic influence of the C-terminal part contributes particularly to the low solvent exposure of the titratable groups, and hence to the low structural stability and propensity for aggregation of the recombinant hIFNgamma. Proteins 2001;43:125-133., (Copyright 2001 Wiley-Liss, Inc.)

Association rate constants for antigen/antibody associations have been computed by Brownian Dynamics simulations of D. L. Ermak and J. A. McCammon, J. Chem. Phys. 69:1352-1360, 1978. The model of monoclonal antibody (mAb) D44.1 is based on crystallographic data (B. C. Braden et al., J. Mol. Biol. 243:767-781, 1994). Electrostatic forces that steer the antigen to the antibody-combining site are computed by solving the linearized Poisson-Boltzmann equation. D44. 1-HEL complex displays very similar association motifs to a related anti-lysozyme antibody, HyHEL-5-HEL system. The computed association rate constants are comparable in the two systems, although the experimental affinity constants differ by three orders of magnitude (D. Tello et al., Biochem. Soc. Trans. 21:943-946, 1993; K. A. Hibbits et al., Biochemistry. 33:3584-3590, 1994). Simulations suggest that the origin of the differences in the affinity come from dissociation rate constants. We have also carried out simulation experiments on a number of mutant antibody fragment-HEL associations to address the role of electrostatics and, to a limited extent, the orientational aspects of association.