04 February 2008

Bacteriophages as a matrix for self-assembly of stable nanostructures

While the development of biomedicine, electronics and other research areas is aimed at the introduction and use of various nanoconstructions, the creation of the necessary nanomaterials still causes difficulties for specialists.

Recently, scientists at The Scripps Research Institute (TSRI) have proposed a new approach to solving this problem, allowing the creation of self-assembling nanoconstructions based on natural proteins. Such designs can be used in a variety of practical applications, from medical screening to microelectronics.

The molecules of natural proteins are folded into uniform three-dimensional structures, but scientists have not been able to reproduce this process until now. The authors proposed the first effective method for the synthesis of such molecules in the laboratory.

Scientists working with the bacteriophage M13 decided to study the possibility of using biologically inert proteins, which make up most of the virus particle, as a matrix for creating nanoconstructions. (According to the proportions, phage M13 corresponds to a pencil 4 feet long, the "rubber band" at the end of which serves to introduce the hereditary material of the virus into the bacterial cell, and the remaining shell proteins are biologically neutral.)

The researchers chemically modified molecular protrusions on the surface of protein molecules, which acquired the property of attracting and binding components necessary for the formation of polyacrylamide fibers, a polymer traditionally used for the manufacture of laboratory gels.

The resulting structure, folding into a spiral resembling a DNA or RNA molecule, took the form of a comb, with polymer molecules acting as teeth. These teeth, in turn, interacted with each other to form an elastic rubber-like protein-polymer conjugate. The resulting material can be divided into layers, but it is almost impossible to break into pieces. In addition, regardless of the compression force, it always restores its original shape due to strong viral proteins acting as reinforcement.

Further analysis revealed additional important characteristics of the new material. The shape of the forming combs is not identical – they differ in the number of teeth. However, in order to form chemical bonds between the teeth, the combs must be located at a strictly defined distance from each other, which ensures the formation of uniform pores, the width of which is 4 nm, and the length is more than 1 microns.

This uniformity is the opposite of the molecular chaos obtained by mixing polymer particles and bacteriophages without pretreatment of the latter.

Despite the fact that the aim of the work was to prove the possibility of using bacteriophages as a matrix, scientists have already proposed several ways to use the resulting nanostructures. The implementation of the proposed ideas will not be difficult for specialists, because phages can be produced in huge quantities without large financial costs, and polymer components are available for commercial use.

Channels of a given size formed by the pores of a new material can be used to move electrons in the development of microelectronic devices. The porous material can also be useful for filtering molecules of a certain size, for example, when testing blood samples for the presence of certain proteins associated with a particular disease. Among the more complex of possible practical applications is the change of biologically active regions of phage particles, which, interacting with specific molecules, will fix them inside the pores of the material.

In order to expand the range of possible applications of new nanoconstructions, the authors have already begun to explore the possibilities of manufacturing new materials based on them.

Article by B. Willis et al. Biologically templated organic polymers with nanoscale order is published in the on-line version of PNAS.

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