Elsevier

Biomaterials

Volume 28, Issue 29, October 2007, Pages 4178-4191
Biomaterials

Leading Opinion
Recent developments in the molecular imprinting of proteins

https://doi.org/10.1016/j.biomaterials.2007.06.017Get rights and content

Abstract

Molecular imprinting is an inexpensive method for the rapid fabrication of organic polymeric and inorganic network-structured materials that selectively bind a template molecule—in other words, materials that function as artificial antibodies. Imprints against small-molecule templates have been generated for decades, but attempts to prepare imprints against proteins have, until recently, been far less successful. The field has progressed rapidly, however, and a number of molecular imprints selective for protein ligands have now been reported. Given the enormous potential of replacing the antibodies used in a host of immunoassays with robust and inexpensive receptors, efforts in this area continue to intensify. This review begins with a brief analysis of two naturally occurring protein–ligand complexes, each of which illustrates the specific interactions essential for precise molecular recognition. Key developments—all appearing in 2006 and 2007—in the molecular imprinting of proteins, including many impressive advances, are then discussed.

Introduction

Natural and synthetic receptors for small-molecule and protein ligands currently find extensive application in both the laboratory and clinic. Antibodies, which can be elicited against essentially any molecule foreign to the host, are the workhorses of natural receptors [1]. Synthetic receptors include those created by the manipulation of biomolecules (e.g. “aptamers” [2]) and by total synthesis (e.g. “hosts” [3]). A technique that allows the rapid and inexpensive generation of synthetic receptors to, in principle, any target molecule is “molecular imprinting.” This approach yields organic polymeric [4], [5] and inorganic network-structured [6] materials that retain a “memory” for a template molecule—in other words, materials that function as artificial antibodies. Extensive work has been done in the field over the past four decades, and a number of comprehensive monographs have been published [7], [8], [9].

Here, the focus will be on the molecular imprinting of proteins. (The imprinting of small molecules has advanced significantly, and a number of companies now sell tailor-made imprints—for example, MIP Technologies AB, Lund, Sweden; POLYIntell, Rouen, France; and Semorex, Inc., North Brunswisk, NJ, USA.) Two reviews of protein imprinting, covering the literature through the end of 2005, have recently appeared [10], [11], and thus only highlights from 2006 to 2007 will be discussed below.

Section snippets

Protein–ligand complexes

Before turning to the details of molecular imprinting, we will examine the specificity that proteins can exhibit for their targets—specificity that is the envy of molecular imprinters. Of course, the robustness of molecular imprints is the envy of proteins, which are (generally) only stable under or near physiological conditions and typically can be employed only once for an assay. And again molecular imprints can be produced rapidly and inexpensively. Nonetheless, the exquisite specificity of

Molecular imprinting

Regardless of the exact approach (and many clever approaches have been developed), essentially all molecular imprints are fabricated by the same general strategy. That employed for the production of an organic imprint—often termed a molecularly imprinted polymer (MIP)—is outlined in Fig. 5. A template molecule is first allowed to interact, either through noncovalent or (reversibly formed) covalent bonds, with functionalized monomers (methacrylate, acrylamide, or styrene derivatives are

The imprinting of proteins

While numerous selective molecular imprints against small molecules have been prepared, efforts to generate imprints against protein targets have, until recently, been far less successful. Creating an imprint with a constellation of functionality complementary to a protein template is obviously a daunting prospect. Additional challenges have included the impeded diffusion of macromolecular species into and out of traditional monolithic imprints; the insolubility of proteins in commonly utilized

Recent work

To address the unimpressive selectivity for proteins typically seen with bulk organic imprints, the Takeuchi group created an array of imprints, which together were used to determine unique binding profiles for a set of analyte proteins [21]. As illustrated in Fig. 7, the monolithic imprints were formed following the “traditional” (meth)acrylate approach. Three proteins—cytochrome c (Cyt), ribonuclease A (Rib), and α-lactalbumin (Lac)—and two functionalized monomers—acrylic acid (AA) and

Conclusions

As the results discussed above clearly demonstrate, molecular imprints can bind proteins specifically and with high affinity. Obviously, the different methods vary enormously in their particulars, and they have (understandably) yet to be systematically compared. Although it is unlikely that any one approach will universally yield the best imprints against all proteins (and for all applications), it does seem clear that thin films have superior properties as compared with bulk monoliths. Also

Acknowledgments

I am most grateful to Professor Sandra Burkett for numerous helpful conversations and to the Amherst College Senior Sabbatical Fellowship Program, funded in part by the H. Axel Schupf’ 57 Fund for Intellectual Life, for financial support. Acknowledgment is also made to the Donors of the American Chemical Society Petroleum Research Fund for support of this research. Finally, I am pleased to thank the reviewers for their many helpful suggestions and Mari Rosen for her help in editing this

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    Editors Note: Leading Opinions: This paper is one of a newly instituted series of scientific articles that provide evidence-based scientific opinions on topical and important issues in biomaterials science. They have some features of an invited editorial but are based on scientific facts, and some features of a review paper, without attempting to be comprehensive. These papers have been commissioned by the Editor-in-Chief and reviewed for factual, scientific content by referees.

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