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A molecular dynamics model of the Bt toxin Cyt1A and its validation by resonance energy transfer by Xiaochuan Li; Kerrick J. Nevels; Zygmunt Gryczynski; Ignacy Gryczynski; Marianne Pusztai-Carey; Dexuan Xie; Peter Butko is a Biochemistry, Genetics and Molecular Biology article available to read on EtoBox.

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Cyt1A is a cytolytic toxin from Bacillus thuringiensis var. israelensis. A computer model of the toxin in solution was generated and validated by resonance energy transfer (RET). The average distance between the two tryptophans (residues 158 and 161) and the fluorescently labeled cysteine 190 was 2.16 nm, which closely matched the distance predicted in computer simulations, 2.2 nm. The simulation results were able to explain two previous experimental observations: (i) amino-acid sequences of all Cyt toxins contain four blocks of highly conserved residues; and (ii) several single-point mutations drastically abrogated Cyt1A's toxicity. Selective randomization of atomic coordinates in the computer model revealed that the conserved blocks are important for proper folding and stability of the toxin molecule. Replacing lysine 225 with alanine, a mutation that renders the toxin inactive, was shown to result in breaking the hydrogen bonds between K225 and V126, L123, and Y189. Calculated Helmholtz free energy difference of the inactive mutation K225A was higher by 12 kcal/mol and 5 kcal/mol than the values for the benign mutations K118A and K198A, respectively, which indicates that the K22

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Author

Xiaochuan Li; Kerrick J. Nevels; Zygmunt Gryczynski; Ignacy Gryczynski; Marianne Pusztai-Carey; Dexuan Xie; Peter Butko

Publisher

Elsevier Science; Elsevier ; Elsevier BV (ISSN 0301-4622)

Published

2009

Language

EN

Field

Biochemistry, Genetics and Molecular Biology (Life Sciences)