Organization of Fusicoccin Receptor in Higher Plant Plasma Membrane: Relationship between Affinity and Molecular Mass

O. I. Klychnikov^1,3, A. V. Drabkin¹, O. V. Vasilenko¹, Yu. S. Pavlov⁵, M. S. Trofimova⁴, I. N. Smolenskaya⁴, A. A. Rozenkranz^1,2, A. S. Sobolev^1,2, and A. V. Babakov^1*

¹Institute of Agricultural Biotechnology, Russian Academy of Agricultural Sciences, Timiryazevskaya ul. 42, Moscow, 127550 Russia; fax: (095) 977-0947; E-mail: avb@agrobio.msk.ru

²Department of Biophysics, School of Biology, Lomonosov Moscow State University, Moscow, 119899   Russia; E-mail: asobol@1.biophys.bio.msk.ru

³Department of Biotechnology, Timiryazev Agricultural Academy, Timiryazevskaya ul. 49, Moscow, 127550 Russia; E-mail: kloleg@glasnet.ru

⁴Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia; E-mail: vladimir@ad.plantphys.msk.ru

⁵Institute of Physical Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 117915 Russia; fax: (095) 128-6912

^* To whom correspondence should be addressed.

Received December 25, 1997; Revision received June 4, 1998

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Higher plant plasma membranes carry receptors of different affinity for the phytotoxin fusicoccin. Reception of fusicoccin involves proteins belonging to the highly conserved 14-3-3 family, but the complete structure of the fusicoccin receptor (FCR) is unknown. Using radiation inactivation analysis, we estimated the molecular masses of low-affinity and high-affinity FCR at 63 ± 7 and 130 ± 15 kD, respectively. The dose dependences of receptor inactivation indicate that microsomal specimens contain "silent" FCRs of 420 ± 90 kD in amounts commensurate with that of the active FCRs. Both low- and high-affinity FCRs are inactivated by hydrolytic enzymes from the outer surface of the plasma membrane, and impairment of protoplast integrity causes an irreversible transition of the low-affinity binding site into the high-affinity one. A scheme is proposed for the organization of different types of FCR in the plasma membrane, implying that the membrane affinity for fusicoccin reflects the interaction between proteins in the FCR complex.

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KEY WORDS: fusicoccin receptor, affinity, molecular mass, radiation inactivation, protoplasts

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