Core-controlled polymorphism in virus-like particles

Departments of ^§Biochemistry and Biophysics and
*Biology, and
^†Microscopy and Imaging Center, Texas A&M University, College Station, TX 77843;
^‡Department of Chemistry and
^¶Indiana Molecular Biology Institute, Indiana University, Bloomington, IN 47405; and
^‖Department of Chemistry, University of Massachusetts, Amherst, MA 01002

Communicated by Charles S. Parmenter, Indiana University, Bloomington, IN, November 29, 2006 (received for review August 8, 2006)

Abstract

This study concerns the self-assembly of virus-like particles (VLPs) composed of an icosahedral virus protein coat encapsulating a functionalized spherical nanoparticle core. The recent development of efficient methods for VLP self-assembly has opened the way to structural studies. Using electron microscopy with image reconstruction, the structures of several VLPs obtained from brome mosaic virus capsid proteins and gold nanoparticles were elucidated. Varying the gold core diameter provides control over the capsid structure. The number of subunits required for a complete capsid increases with the core diameter. The packaging efficiency is a function of the number of capsid protein subunits per gold nanoparticle. VLPs of varying diameters were found to resemble to three classes of viral particles found in cells (T = 1, 2, and 3). As a consequence of their regularity, VLPs form three-dimensional crystals under the same conditions as the wild-type virus. The crystals represent a form of metallodielectric material that exhibits optical properties influenced by multipolar plasmonic coupling.

Footnotes

**To whom correspondence should be addressed. E-mail: dragnea{at}indiana.edu
Author contributions: C.C.K. and B.D. designed research; J.S., C.D., M.-C.D., and C.C. performed research; K.G., B.S., M.D., and V.M.R. contributed new reagents/analytic tools; J.S., C.D., A.M., and A.H. analyzed data; and B.D. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0610542104/DC1
Abbreviations:

VLP,

virus-like particle;

PEG,

polyethylene glycol;

BMV,

brome mosaic virus;

CP,

capsid protein;

AFM,

atomic force microscopy.