1NMR Laboratory, Institute of Chemical Technology in Prague, Technická, 5, CZ-166 28, Czech Republic
2Department of Biochemistry and Microbiology, Institute of Chemical Technology in Prague, Technická, 5, CZ-166 28, Czech Republic
Matrix proteins (MA) play an important role in the assembly of immature viral particles in retroviruses as well as in their transportation to the cell membrane and budding. Mason-Pfizer monkey virus (M-PMV) belongs to the family of so called D-type retroviruses, which are characterized by a different mechanism of immature capsid assembly when compared with the C-type retroviruses (HIV-1). However, a replacement of arginine in the position 55 for phenylalanine in the amino acid sequence of the matrix protein results in the changed morphogenesis and the virus behaves similarly as HIV-11.
We started structural and dynamical studies on the R55F mutant of M-PMV MA protein to look for relations between such substantial changes of the behavior of the virus and possible changes in three-dimensional structure of the matrix protein. Doubly labeled (13C/15N) protein was expressed and purified for NMR experiments. Almost complete resonance assignment was achieved by using triple resonance NMR experiments and based on the calculation of chemical shift index four helical motifs were located. Further experimental NMR data (NOE interactions, J-couplings...) were used to calculate the three-dimensional structure of the R55F mutant. Dynamical behavior of the protein was estimated on the basis of measurements of relaxation parameters of 15N nuclei.
Comparison of the solution structures of the R55F mutant with the solution structure of the wt matrix2 revealed a different orientation of the N-terminal half of the structural motif, which is formed by helices I and II. HIV-1 MA has been shown to form trimers3, which might be the biologically relevant species. Molecular modeling was used to compare the propensity to form trimers of both structural motifs, i.e. wt MA and R55F, respectively.
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3. C.P. Hill, D. Worthylake, D.P. Bancroft, A.M. Christensen, W.I. Sundquist: Proc. Natl. Acad. Sci. USA, 1996, 93, 3099-3104