Journal:CHEMBIOINT:1
From Proteopedia
The four-helix bundle in cholinesterase dimers: structural and energetic determinants of stabilityDana A. Novichkova, Sofya V. Lushchekina, Orly Dym, Patrick Masson, Israel Silman and Joel L. Sussman [1] Molecular Tour : pink, hAChE (PDB ID 4ey4); gray, mAChE (PDB ID 1j06); blue, TcAChE (PDB ID 1w76); green, DmAChE (PDB ID 1qo9). . All crystal structures of AChE deposited in the PDB (https://www.rcsb.org) display dimers in which the monomers associate through an antiparallel four-helix bundle. With respect to BChE, crystal structures have been obtained only for monomeric forms of hBChE. In the first hBChE crystal structure obtained (PDB ID 1p0i), of partially glycosylated enzyme expressed in CHO cells, dimers assembling via a . Subsequently, however, a (PDB ID 4aqd) was obtained for fully glycosylated hBChE expressed in Drosophila S2 cells. This dissimilarity of the two crystal structures reveals the high sensitivity of hBChE dimerization to the expression system and crystallization conditions. In silico alanine screening (FEP method) for hAChE. . The amino acids, which substitution by alanine led |ΔΔG|>1 kcal/mol are shown and colored in green or red. . These scenes show that in the case of hAChE, stabilization occurs with both hydrophobic residues of helices, and the salt bridge, and electrostatic interactions on helices. Mutations of His381 and Phe531 to alanine are advantageous. , and their interactions appear to be stabilizing. In silico alanine screening (FEP method) for BChE. . The amino acids, which substitution by alanine led |ΔΔG|>1 kcal/mol are shown and colored in green or red. . BChE has less stabilizing amino acids in loops compared to hAChE. Amino acids unfavorable for BChE dimerization are 1) polar ones (i.e., serine) instead of hydrophobic in helices 2) not exposed to the contact interface (Leu370) 3) Asp375 and Asp378, which repel each other and destabilize the loop. His372 in BChE (analog of His381 in hAChE) forms hydrogen bond with Gln518, and is more buried from the dimerization interface, thus it does not have the destabilizing effect observed in hAChE. Generally, in silico alanine screening shows that hAChE has less amino acid residues with high contribution to both stabilization and destabilization of the dimer, rather than BChE. In spite of a few residues on helices of BChE, extrahelical loops contribute to destabilization of the dimer. . Red loop — first macrostate, blue loop — second macrostate, green loop — third macrostate, yellow loop - forth macrostate. .  BChE 374-382 loop:
This study was supported by Russian Foundation for Basic Research (project №19-03-00043). References
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