Lin Yan

The interaction of proteins and cells with self-assembled monolayers of alkanethiolates on gold and silver

Alkanethiols, HS(CH2)nX, chemisorb on gold and silver and form self-assembled monolayers (SAMs). The ability to present a variety of functional groups, X, at the terminal position of the alkanethiol makes it possible to control the structure of the surface at the molecular level, and thus to control the interfacial properties of these organic surfaces. These SAMs constitute an exceptionally useful set of model surfaces with which to study the interaction of synthetic materials with biologically relevant systems. By varying the terminal group X, it is possible to examine the influence of the structure and polarity of common organic groups on the adsorption of proteins. Alkanethiols terminated with oligo(ethylene glycol) groups form SAMs that resist the adsorption of proteins (so-called ‘inert surfaces’). These alkanethiols, when used in mixed SAMs that include alkanethiols that present other functional groups, isolate the biomolecular interactions of interest from non-specific effects and simplify fundamental studies of protein adsorption. Surface plasmon resonance (SPR) is a particularly valuable technique for measuring rates and equilibrium constants of processes that involve adsorption of proteins at surfaces and for characterizing mechanisms of protein adsorption. Since the techniques used in preparing SAMs for studies of protein adsorption are essentially the same as those used in preparing substrates for SPR, a common synthetic technology can be used with both. Soft lithographic techniques—microprinting and micromolding—make it possible to pattern SAMs with different functionalities on surfaces that can be either planar or contoured. The combination of SAMs, inert surfaces, SPR, and soft lithography allows the study of the molecular-level interaction of solutions containing proteins with synthetic surfaces. Extensions of these studies to investigations of the attachment and spreading of cells on surfaces also offer a new set of research tools in cell biology.

Parallel Synthesis and Screening of a Solid Phase Carbohydrate Library

A solid phase carbohydrate library was synthesized and screened against Bauhinia purpurea lectin. The library, which contains approximately 1300 di- and trisaccharides, was synthesized with chemical encoding on TentaGel resin so that each bead contained a single carbohydrate. Two ligands that bind more tightly to the lectin than Gal-β-1,3-GalNAc (the known ligand) have been identified. The strategy outlined can be used to identify carbohydrate-based ligands for any receptor; however, because the derivatized beads mimic the polyvalent presentation of cell surface carbohydrates, the screen may prove especially valuable for discovering new compounds that bind to proteins participating in cell adhesion.

Biological surface engineering: a simple system for cell pattern formation

Biological surface engineering using synthetic biological materials has a great potential for advances in our understanding of complex biological phenomena. We developed a simple system to engineer biologically relevant surfaces using a combination of self-assembling oligopeptide monolayers and microcontact printing (muCP). We designed and synthesized two oligopeptides containing a cell adhesion motif (RADS)n (n = 2 and 3) at the N-terminus, followed by an oligo(alanine) linker and a cysteine residue at the C-terminus. The thiol group of cysteine allows the oligopeptides to attach covalently onto a gold-coated surface to form monolayers. We then microfabricated a variety of surface patterns using the cell adhesion peptides in combination with hexa-ethylene glycol thiolate which resist non-specific adsorption of proteins and cells. The resulting patterns consist of areas either supporting or inhibiting cell adhesion, thus they are capable of aligning cells in a well-defined manner, leading to specific cell array and pattern formations.

Self‐Assembled Monolayers (SAMs) and Synthesis of Planar Micro‐ and Nanostructures

Abstract A polymer is a macromolcule made up of multiple equivalents of one or more monomers linked together by covalent bonds. Self‐assembled monolayers (SAMs) are highly ordered molecular assemblies formed by chemisorption of functionalized molecules on the surface. Various system of SAMs are reviewed in this article. The synthesis and structures of SAMs on gold and silver are briefly discussed along with chemical reactions that occur on SAMs after their assembly. The patterning of SAMs on gold and its applications are discussed in the plane of the monolayer. #Reprinted from Supramolecular Polymers, Ciferri, A., Ed., Marcel Dekker, Inc.: New York, 2000; 435–470.

Isomorphous binding of mercury-substituted thiosaccharides to pertussis toxin crystals yields crystallographic phases

An isomorphous derivative of pertussis toxin crystals was prepared using a 2-alpha-mercuric analog of N-acetyl neuraminic acid in a method analogous to the use of inhibitors labelled with heavy atoms to solve crystal structures of enzymes. This derivative exploits the specific binding between pertussis toxin and terminal sialic acid residues on receptor glycoproteins. Difference Patterson maps yielded heavy-atom sites which refined with good statistics, indicating that the protein probably does not undergo a conformational change on receptor binding. Mercuric analogs of other monosaccharides should be easily obtainable using the same synthetic strategy, suggesting a general method for derivatizing crystals of carbohydrate-binding proteins.