Ordered arrays of proteins on graphite observed by scanning tunneling microscopy

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Abstract
Two globular proteins, lysozyme and chymotrypsinogen A, were imaged on graphite using a scanning tunneling microscope. In contrast to the isolated molecules typically seen, long-range order was observed in both of these systems when the protein concentration of the solution deposited on the graphite was sufficient for multilayer coverage. For lysozyme, regular two-dimensional arrays of protein molecules were seen, with periodicities ranging from about 40 (the approximate size of a lysozyme molecule) to about 150 Å. These length scales depend on the lysozyme concentration in the initial solution. For chymotrypsinogen A, two-dimensional structures that covered a much smaller area of the graphite were observed. The structural features observed suggest such possibilities as protein structure determination using surface structural techniques and epitaxial growth of protein crystals on these two-dimensional structures.