RESUMEN
Responsible for synthesizing the complementary strand of the DNA template, DNA polymerase is a crucial enzyme in DNA replication, recombination and repair. A highly conserved tyrosine (Tyr), located at the C-terminus of the O-helix in family A DNA polymerases, plays a critical role in enzyme activity and fidelity. Here, we combined the technology of genetic code extension to incorporate non-canonical amino acids and molecular dynamics (MD) simulations to uncover the mechanisms by which Tyr671 impacts substrate binding and conformation transitions in a DNA polymerase from Thermus aquaticus. Five non-canonical amino acids, namely l-3,4-dihydroxyphenylalanine (l-DOPA), p-aminophenylalanine (pAF), p-acetylphenylalanine (pAcF), p-cyanophenylalanine (pCNF) and p-nitrophenylalanine (pNTF), were individually incorporated at position 671. Strikingly, Y671pAF and Y671DOPA were active, but with lower activity compared to Y671F and wild-type. Y671pAF showed a higher fidelity than the Y671F, despite both possessing lower fidelity than the wild-type. Metadynamics and long-timescale MD simulations were carried out to probe the role of mutations in affecting protein structure, including open conformation, open-to-closed conformation transition, closed conformation, and closed-to-open conformation transition. The MD simulations clearly revealed that the size of the 671 amino acid residue and interactions with substrate or nearby residues were critical for Tyr671 to determine enzyme activity and fidelity.
Asunto(s)
Simulación de Dinámica Molecular , Polimerasa Taq , Tirosina , Tirosina/química , Tirosina/genética , Tirosina/metabolismo , Polimerasa Taq/metabolismo , Polimerasa Taq/química , Polimerasa Taq/genética , Thermus/enzimología , Thermus/genética , Aminoácidos/química , Aminoácidos/metabolismo , Aminoácidos/genética , Conformación Proteica , Especificidad por Sustrato , CinéticaRESUMEN
Two new hexenol glycosides, (Z)-hex-3-en-1-ol O-ß-d-xylcopyranosyl-(1-6)-ß -d-glucopyranosyl-(1-2)-ß-d-glucopyranoside (1) and (E)-hex-3-en-1-ol O-ß-d-xylcopyranosyl-(1-6)-ß-d-glucopyranosyl-(1-2)-ß-d-glucopyranoside (2), were isolated from the 50% ethanol elution of macroporous resin of Physalis alkekengi var. franchetii. Their structures were established by detailed spectroscopic analysis, including extensive 2D-NMR data. This is the first time to report the (Z) and (E) 3-hexenol glycosides from Physalis alkekengi var. franchetii.