High-resolution NMR studies of encapsulated proteins in liquid ethane

Many of the difficulties presented by large, aggregation-prone, and membrane proteins to modern solution NMR spectroscopy can be alleviated by actively seeking to increase the effective rate of molecular reorientation. An emerging approach involves encapsulating the protein of interest within the protective shell of a reverse micelle and dissolving the resulting particle in a low viscosity fluid, such as the short chain alkanes. Here we present the encapsulation of proteins with high structural fidelity within reverse micelles dissolved in liquid ethane. The addition of appropriate cosurfactants can significantly reduce the pressure required for successful encapsulation. At these reduced pressures, the viscosity of the ethane solution is low enough to provide sufficiently rapid molecular reorientation to significantly lengthen the spin-spin NMR relaxation times of the encapsulated protein.     

Structure, function, and antigenicity of cholera toxin.

Chemical modification of intact cholera toxin or its B subunit by either partial nitration or reduction and alkylation did not result in significant loss of biological activity as determined by measurement of cyclic AMP in Chinese hamster ovary cells. Complete nitration or succinylation in the presence of guanidine hydrochloride resulted in complete loss of biological activity and significantly affected the immunoreactivity of the toxin and B subunit. Compositional analyses of both the isolated alpha and gamma chains of the toxin were typical of globular proteins and did not reveal significant hydrophobicity. Analysis of antigenic relationships by radioimmunoassay indicated a partial crossreactivity between the alpha chain and the B subunit of cholera toxin. Since previous structural studies of the beta chain of cholera toxin indicated chemical similarity with the glycoprotein hormones [Kurosky et al. Science 195:299 (1977)], radioimmunoassay procedures were employed to investigate for possible crossreactivity. No evidence of crossreactivity between cholera toxin subunits and subunits of ovine luteinizing hormone was found.     

Evaluation of moment statistics for molecular modeling

The concept of moment statistics for evaluating conformations of molecules derived from molecular dynamics simulations is presented. A comparison of the rigidity of tetralin with benzene and cyclohexane, the effect of “tooth thickness” in geared systems, the fluctional motion of a linear alkane, and the differences between dynamical motions of hydrogen-bonded systems in gas versus solution phases were studied. The strengths and weaknesses of implementing moment statistics as a tool for data reduction are described. © 1995 by John Wiley & Sons, Inc.     

A continuous space-time finite element method for the wave equation

We consider a finite element method for the nonhomogeneous second-order wave equation, which is formulated in terms of continuous approximation functions in both space and time, thereby giving a unified treatment of the spatial and temporal discretizations. Our analysis uses primarily energy arguments, which are quite common for spatial discretizations but not for time.

We present a priori nodal (in time) superconvergence error estimates without any special time step restrictions. Our method is based on tensor-product spaces for the full discretization.

     

Fractal properties of the singular function s(u)

The function s(u) arising in the study of long primitive BCH codes over GF(q) is reviewed. The set of points 0 < u 1 such that q ^ku has a modulo 1 representation in the interval [a, 1] for every integer k 0 is shown to have Hausdorff dimension s(a) for every 0 a 1. Berlekamp's conjecture on the dimension of a set of points at which s fails to be differentiable is also proved.