Biomaterial rejection is linked to the initial protein adsorption upon contact with foreign materials with body fluids. Our objective is to minimize or control protein and biological interactions with new materials through the tailored manipulation of the molecular forces controlling the outcomes of encounters between foreign materials and biological fluids. Using a combination of direct force measurements, biochemical methods, and molecular modeling, we are quantifying the relationship between molecular surface structure and composition, surface forces, and protein adsorption. These data are intended to guide the design of new, effective biocompatible materials.

Cell adhesion is mediated and modulated through contacts involving chemical moieties on cell surfaces. In particular, the enhanced expression of certain glycolipids on cancer cells may determine their metastatic potential. The significance of specific glycolipid interactions, however, is linked directly to the strengths of the molecular forces governing the resulting adhesion. We are using direct force measurements, fluorescence microscopy, and light scattering to quantify the magnitudes and ranges of glycolipid-mediated adhesive forces and to determine the impact of those forces on the strengths of glycolipid-mediated membrane attachments. We are testing directly the role of membrane surface components in cell adhesion and the potential utility of therapeutics designed to block their interactions.

Many biosensor designs are based on the selective binding of soluble analyte to immobilized receptors. The surface microenvironment can, however, significantly affect sensor performance. We are currently quantifying changes in protein-binding strengths in response to interfacial perturbations. Furthermore, kinetic modeling of site-selective adsorption data have demonstrated that subtle interfacial perturbations impact sensor performance. Our objective is to determine the molecular basis of altered protein function by the surface microenvironment and to optimize sensor performance through the tailored manipulation of the transducer surface properties.

Protein surface topology plays a major role in modulating the rates of protein-binding events. We are using direct force measurements to probe the impact of local protein structural motifs on the forces that control the rates of protein collisions. In particular, we are investigating the impact of surface charge distributions and protein orientation on protein electrostatic surface properties and resulting protein interactions. Use of both wild type and engineered proteins permits precise control of the surface region probed. Measurements are compared with theoretical calculations. The functional implications of these findings are being investigated by Brownian dynamics simulations and kinetic measurements.

A novel system has been developed to engineer proteins to have desirable binding properties. Genetic fusions to a cell wall protein allow the protein of interest to be tethered to the cell surface and probed for binding to fluorescently labeled targets. Introduction of diversity into a population by mutagenesis is followed by isolation of desirable mutations by flow cytometry and sorting.

The purpose of this work is to measure and manipulate the redox regulation of yeast's secretory pathway in order to improve production yields of pharmaceutical proteins. Genetic, biochemical, and fermentor operation strategies will be implemented to alter the cellular processing of disulfides, covalent crosslinks which stabilize the folded structure of a protein.

The goal of this project is to examine the kinetics of protein processing in the secretory pathway in order to identify the mechanistic steps which limit the yield and rate of protein secretion. The ultimate goal is to use this information to rationally design improved production systems for phamaceutical proteins.