Macroscopic Aggregation of Tobacco Mosaic Virus Coat Protein

V. N. Orlov¹, A. M. Arutyunyan¹, S. V. Kust¹, E. A. Litmanovich², V. A. Drachev¹, and E. N. Dobrov^1*

¹Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3181; E-mail: dobrov@pcman.genebee.msu.su

²Department of Polymer Sciences, School of Chemistry, Lomonosov Moscow State University, Moscow, 119899 Russia

^* To whom correspondence should be addressed.

Received October 5, 2000; Revision received November 5, 2000

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The relationship between processes of thermal denaturation and heat-induced aggregation of tobacco mosaic virus (TMV) coat protein (CP) was studied. Judging from differential scanning calorimetry “melting” curves, TMV CP in the form of a trimer-pentamer mixture (“4S-protein”) has very low thermal stability, with a transition temperature at about 40°C. Thermally denatured TMV CP displayed high propensity for large (macroscopic) aggregate formation. TMV CP macroscopic aggregation was strongly dependent on the protein concentration and solution ionic strength. By varying phosphate buffer molarity, it was possible to merge or to separate the denaturation and aggregation processes. Using far-UV CD spectroscopy, it was found that on thermal denaturation TMV CP subunits are converted into an intermediate that retains about half of its initial alpha-helix content and possesses high heat stability. We suppose that this stable thermal denaturation intermediate is directly responsible for the formation of TMV CP macroscopic aggregates.

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KEY WORDS: tobacco mosaic virus coat protein, thermal denaturation, partially folded intermediate, aggregation, circular dichroism, differential scanning calorimetry

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