Combined molecular dynamics and continuum solvent studies of the pre-pore Cry4Aa trimer suggest its stability in solution and how it may form pore.
Cry4Aa toxin is one of the highly specific mosquito-larvicidal proteins produced by the bacterium Bacillus thuringiensis subspecies israelensis. It is thought to form pores in the larval midgut membrane that cause membrane leakage and subsequent insect death. Therefore, Cry4Aa and other Cry toxins have been used as efficient and safe bacterial insecticides to control the disease-carrying mosquitoes such as Aedes, Anopheles, and Culex. However, we still do not clearly understand how Cry toxins kill mosquito-larvae at molecular details. Recent electron crystallographic images of Cry4Ba toxin, another toxin closely related to Cry4Aa toxin, have suggested that the protein forms trimer in aqueous solution and in lipid monolayer. Moreover, the unit cell of X-ray crystal structure of Cry4Ba toxin has been shown to be trimeric. In this study, we constructed the first full-atom structural model of Cry4Aa trimer using the trimeric unit cell structure of Cry4Ba toxin as a template and then used the methods of molecular dynamics (MD) and molecular mechanics combined with Poisson-Boltzmann and surface area (MM-PBSA) to show that the trimeric structure of Cry4Aa toxin is stable in 150 mM KCl solution on 10 ns timescale. The results reveal that Cry4Aa toxins use polar amino acid residues on alpha-helices 3, 4, and 6 to form trimer and suggest that the proteins form trimer to reduce their non-polar interactions with surrounding water. Based on the obtained trimeric structure of Cry4Aa toxins, we propose that pore formation of Cry toxins may involve a 90 degrees -hairpin rotation during the insertion of their three alpha4-alpha5 hairpins into the membrane. This process may be mediated by water and ions.PACS Codes: 87.15.ap, 87.15.bk, 87.14.ep.
Taveecharoenkool
Taveechai
T
Theoretical and Computational Biophysics Laboratory, Department of Physics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand. fscicpk@ku.ac.th.
Angsuthanasombat
Chanan
C
Kanchanawarin
Chalermpol
C
J Mol Graph. 1996 Feb;14(1):33-8, 27-8
8744570
Biochem Biophys Res Commun. 2007 Oct 5;361(4):890-5
17681273
J Biol Chem. 2007 Jul 20;282(29):21222-9
17537728
J Comput Chem. 2005 Dec;26(16):1781-802
16222654
Proteins. 2008 Feb 15;70(3):834-43
17729286
Annu Rev Genet. 2003;37:409-33
14616068
Mol Microbiol. 1999 Jan;31(2):463-71
10027964
J Mol Biol. 1999 Apr 16;287(5):1011-22
10222207
J Comput Chem. 2004 Jan 30;25(2):238-50
14648622
Acta Crystallogr D Biol Crystallogr. 2001 Aug;57(Pt 8):1101-9
11468393
Appl Environ Microbiol. 2001 Jan;67(1):323-9
11133462
Bioinformatics. 2008 Dec 1;24(23):2780-1
18818215
J Phys Chem B. 1998 Apr 30;102(18):3586-616
24889800
Microbiol Mol Biol Rev. 1998 Sep;62(3):807-13
9729610
Biochem Biophys Res Commun. 2005 May 6;330(2):519-25
15796913
Appl Environ Microbiol. 2002 Jan;68(1):194-200
11772627
Appl Environ Microbiol. 1999 Oct;65(10):4513-20
10508083
Adv Protein Chem. 2003;66:27-85
14631816
Appl Environ Microbiol. 1999 May;65(5):1900-3
10223976
J Biochem Mol Biol. 2004 May 31;37(3):304-13
15469711
Nature. 1991 Oct 31;353(6347):815-21
1658659
Structure. 1998 Apr 15;6(4):421-7
9562553
Structure. 2001 May 9;9(5):409-17
11377201
J Mol Biol. 1995 Dec 1;254(3):447-64
7490762
Biochim Biophys Acta. 2002 Dec 23;1567(1-2):113-22
12488044
J Biochem Mol Biol. 2006 May 31;39(3):270-7
16756755
J Bacteriol. 2006 May;188(9):3391-401
16621834
Microbiol Mol Biol Rev. 1998 Sep;62(3):775-806
9729609
J Mol Biol. 2003 Jul 18;330(4):891-913
12850155
J Biol Chem. 2000 Aug 4;275(31):23602-7
10811807
J Invertebr Pathol. 2006 Jul;92(3):172-7
16777138
Appl Environ Microbiol. 1994 Oct;60(10):3711-7
7527203
Proc Natl Acad Sci U S A. 1998 Oct 13;95(21):12289-94
9770479
Proc Natl Acad Sci U S A. 2002 May 28;99(11):7432-7
12032300
Peptides. 2008 Feb;29(2):318-23
18226424
J Mol Biol. 2005 Apr 29;348(2):363-82
15811374
Acc Chem Res. 2000 Dec;33(12):889-97
11123888