Nonstatistical binding of a protein to clustered carbohydrates

Nonstatistical binding of a protein to clustered carbohydrates

^*Department of Chemistry, Princeton University, Princeton, NJ 08544; and ^†Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138

Contributed by George M. Whitesides

Abstract

Carbohydrate-derivatized self-assembled monolayers (SAMs) are used as a model system to address issues involving cell-surface carbohydrate–protein interactions. Here we examine the influence of carbohydrate surface density on protein-binding avidity. We show that the binding selectivity of Bauhinia purpurea lectin switches from one carbohydrate ligand to another as the surface density of the carbohydrate ligands increases from values of χ_sugar ≈ 0.1–1.0. Polyvalent binding is possible at all surface densities investigated; hence, the switch in selectivity is not due simply to the achievement of a critical density that permits polyvalent contacts. Instead, secondary interactions at high surface densities promote a switch in carbohydrate-binding selectivity. These findings may have implications for how changes in the composition and the density of cell-surface carbohydrates influence biological recognition processes and regulatory pathways.

Footnotes

↵ ‡ To whom reprint requests should be addressed. E-mail: dkahne{at}princeton.edu.
Abbreviations:

SAMs,

self-assembled monolayers;

SPR,

surface plasmon resonance;

BP lectin,

Bauhinia purpurea lectin;

RU,

resonance units, DMF, N,N-dimethylformamide;

TEA,

triethylamine;

TFA,

trifluoroacetic acid;

RT,

room temperature