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Ordered Two-Dimensional Hexagonal Arrays Formed from Extremophilic Heat Shock Proteins

Andrew McMillan*, Hiromi Kagawa, Takuro Yaoi, Chad Paavola, Rakesh Mogul, Meyya Meyyappan, and Jonathan Trent

Astrobiology Technology Branch, NASA Ames Research Center,
Moffett Field, CA 94035 USA

This is an abstract for a presentation given at the
Ninth Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is available on the web.


Proteins that self assemble into highly ordered two- and three-dimensional structures are of interest in the field of Nanotechnology for patterned array formation and directed molecular deposition. The molecular chaperone (HSP60) from the hyperthermophilic acidophilic archeon Sulfolobus shibatae can be induced to self-assemble into ordered structures in vitro. The proposed active form in vivo, however, is a 1.1 MD hetero-oligomeric double ring assembly that is comprised of 16-18 ~60 kD subunits (designated a, b and g). A top view of this double torroidal structure reveals an outer ring diameter of approximately 16 nm with an inner core diameter of approximately 10 nm (figure inset, double arrows). In the presence of ATP and Mg2+, these double ring structures self-assemble into extended arrays of either filaments or two-dimensional crystals, depending on both the ATP/Mg2+ concentrations and incubation temperatures. Recent experiments have shown that the b subunit alone can be induced to form these higher ordered structures in a similar concentration dependent manner. We have cloned the b subunit into an E. coli expression vector in order to facilitate large-scale protein expression and to enable the genetic engineering of localized sites along the polypeptide backbone. A portion of the DNA coding for a central loop region in the apical domain of b (figure inset, single arrow) has been removed, thus producing a b-variant that forms into two-dimensional crystals but not filaments, regardless of ATP and Mg2+ concentrations (figure). This "loopless" mutant polypeptide hexagonally packs in a trigonal lattice, exposing the 10 nm hollow core of each double ring with a regular periodic spacing of 16 nm. Two-dimensional crystals formed onto substrates can be used to form homogeneous patterned arrays of selectively bound molecules with high-order periodicity. Investigations into the formation of ordered, monomolecular two-dimensional arrays of crystals onto surfaces with long-range order will be discussed, as well as efforts to preferentially attach colloidal gold and other molecules within the hollow centers of the rings assembled onto inorganic substrates.

micrograph with diagram inset

Abstract in RTF format 4,774 bytes

*Corresponding Address:
Andrew McMillan
Astrobiology Technology Branch, NASA Ames Research Center
Mail Stop 239-15, Moffett Field, CA 94035 USA
phone: 650 604 0474
fax: 650 604 1092


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