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X P Dai

Publications and source records attributed to X P Dai.

6 recordsLinked to original sources
PubMed1994

Crystal structure of the tenth type III cell adhesion module of human fibronectin.

The crystal structure of the cell adhesion module of fibronectin (FNIII10) has been determined at 1.8 A resolution. A recombinant fragment corresponding to the tenth type III module of human fibronectin was crystallized in space group P2(1) with a = 30.7, b = 35.1 and c = 37.7 A and beta = 107 degrees. The structure was determined by molecular replacement and refined by least squares methods. The crystallographic R-factor for the final model of the 91 amino acid module plus 56 solvent atoms is 0.18 for 10 to 1.8 A data. The module consists of two layers of beta-sheet, one with three antiparallel strands and the other with four antiparallel strands. The beta-sheets enclose a hydrophobic core of 24 amino acid side-chains. The module contains the RGD cell recognition sequence in a flexible loop connecting two beta-strands. The tertiary structure of the FNIII10 module has been used to develop a structure-based sequence alignment of 17 type III modules in fibronectin based on the striking conservation of homologous hydrophobic residues. A similar pattern of homologous alternating hydrophobic residues is also evident in a comparison of type III modules in proteins unrelated to fibronectin such as cytokine receptors and muscle proteins.

Amino Acid Sequence↗
PubMed1991

Crystallization and preliminary X-ray analysis of the lactose-specific phosphocarrier protein IIAlac of the phosphoenolpyruvate: sugar phosphotransferase system from Staphylococcus aureus.

The IIA constituent of the lactose permease from Staphylococcus aureus has been crystallized in two different forms. Crystals of form I have been grown from polyethylene glycol 4000 with beta-octyl glucoside. They diffract to 3.0 A resolution and belong to space group C2 with unit cell dimensions a = 141.7 A, b = 130.7 A, c = 96.5 A and beta = 96.2 degrees. Form II crystals have been obtained from a solution containing polyethylene glycol 400, ammonium sulfate and manganese chloride. They diffract to at least 2.8 A resolution and belong to space group P2(1)2(1)2(1) with unit cell dimensions a = 89.9 A, b = 101.5 A and c = 90.9 A.

Escherichia coli Proteins↗
PubMed1990

Crystal structure of an HIV-binding recombinant fragment of human CD4.

CD4 glycoprotein on the surface of T cells helps in the immune response and is the receptor for HIV infection. The structure of a soluble fragment of CD4 determined at 2.3 A resolution reveals that the molecule has two intimately associated immunoglobulin-like domains. Residues implicated in HIV recognition by analysis of mutants and antibody binding are salient features in domain D1. Domain D2 is distinguished by a variation on the beta-strand topologies of antibody domains and by an intra-sheet disulphide bridge.

Amino Acid Sequence↗
PubMedDate not supplied

Pressure and flux profiles in bead-filled ultrafiltration/microfiltration hollow fiber membrane modules.

A general mathematical model for the prediction of pressure, flow rate, and flux profiles in an ultrafiltration/microfiltration hollow fiber membrane module whose shell side is filled with beads has been developed. The model was studied for a variety of operational modes in such modules, e.g., ultrafiltration/microfiltration, permeate flow rate control, Starling flow (encountered in hollow fiber bioreactors), and tube-side elution (encountered in filtration-cum-chromatography processes), etc., with or without a bead-filled extended section at the permeate outlet. An algorithm is provided to determine the model parameters from experimental data using the model equations. The solutions developed have been used to study the uniformity of transmembrane pressure profile along the module length using a quantity called the uniformity factor alpha. This factor shows that the model can be a useful tool for achieving the desired module performance in a number of quite different applications. The model predicts successfully the nature of the transmembrane pressure profile and the solvent flux profile in situations that are quite different, namely, conventional ultrafiltration and Starling flow. The approach used in this study can also be adopted to develop a model for description of other operational modes such as backflushing and shell-side elution used in the processes of filtration-cum-chromatography. Those applications employing similar device configurations may also use this model to predict the pressure and flux profiles to facilitate the design of the process and the operation conditions.

Membranes, Artificial↗
PubMedDate not supplied

An integrated process for biomolecule isolation and purification.

Biomolecule isolation and purification from a fermentation broth usually involve centrifugation, filtration, adsorption, and chromatography steps. Each step contributes to the product cost and product loss. In this research, a cyclic process integrating commercially available ultrafiltration membranes and chromatographic resin beads was developed to achieve the same goal in one device. The device consisted of ion exchange beads on the shell side of a hollow fiber ultrafiltration module. Loading of proteins on the stationary phase on the shell side was carried out for a period of 5-20 min from the permeate on the shell side produced from tube-side feed in ultrafiltration. The eluent was then introduced either from the shell-side inlet or tube-side inlet; the chromatographic fractions were collected from the shell-side outlet. The column was regenerated/washed next to start a new cycle. Systems studied in this cyclic process include the following binary mixtures: myoglobin and beta-lactoglobulin; hemoglobin and bovine serum albumin; and myoglobin and alpha-lactalbumin. Excellent resolutions of the proteins were obtained. A yeast-based cellular suspension containing a mixture of myoglobin and alpha-lactalbumin was also applied to this device. The target proteins were recovered and purified successfully. The cyclic process-based device integrates clarification, concentration, and chromatographic purification of biomolecules and is suitable for both extracellular and intracellular products.

Animals↗