The photosynthetic reaction center (RC) of Rb. sphaeroides catalyzes light-induced electron transfer events which are connected to the conformational dynamics of the protein. The light-induced charge separation between the primary donor (P) and the quinone acceptor (QA) is stabilized by solvent/protein conformational rearrangements. After a laser pulse P+QA recombination, which occurs with a lifetime t~100 ms in room temperature solutions, is accelerated (t~20 ms) at cryogenic temperatures [1] and in dehydrated glassy matrices at room temperature [2]. After prolonged photoexcitation, a slow phase of recombination (t~250 s) is observed, attributed to additional conformational changes [3]. Differential FTIR bands of water associated with the QA/QA transition have been observed upon continuous illumination, leading to propose that weakly bound water molecules plays a role in P+QA stabilization [4]. By controlling the hydration level of RC-detergent films, through equilibration at given relative humidities (r), a strong inhibition of the P+QA conformational stabilization has been observed at low hydration [5]. We compared FTIR light-minus-dark (P+QA/ PQA) differential spectra in hydrated (r=76%) and dehydrated (r=11%) RC films over the 4000- 1000 cm-1. The spectra differ significantly in the 3750-3550 cm-1 range, the band attributed to weakly hydrogen bonded water molecules [5] being strongly reduced in the dried film. Dehydration also affects the 1800-1200 cm-1 range, which includes contributions from P, the quinones and the peptide. Optical absorption measurements performed under the same photoexcitation regime reveal a slow (t~5 s) kinetic component of P+QA recombination which disappears in the dehydrated sample, indicating at low r a destabilization of the charge separated state. As a whole the data suggest a correlation between the hydration shell dynamics and the conformational RC dynamics which stabilize the charge separated state.
Francia F., Mezzetti A., Malferrari M., Venturoli G. (2012). Dehydration affects the stability of primary charge separation in bacterial reaction centers: Studies by optical and differential FTIR spectroscopy. Elsevier [10.1016/j.bbabio.2012.06.386].
Dehydration affects the stability of primary charge separation in bacterial reaction centers: Studies by optical and differential FTIR spectroscopy
FRANCIA, FRANCESCO;MALFERRARI, MARCO;VENTUROLI, GIOVANNI
2012
Abstract
The photosynthetic reaction center (RC) of Rb. sphaeroides catalyzes light-induced electron transfer events which are connected to the conformational dynamics of the protein. The light-induced charge separation between the primary donor (P) and the quinone acceptor (QA) is stabilized by solvent/protein conformational rearrangements. After a laser pulse P+QA recombination, which occurs with a lifetime t~100 ms in room temperature solutions, is accelerated (t~20 ms) at cryogenic temperatures [1] and in dehydrated glassy matrices at room temperature [2]. After prolonged photoexcitation, a slow phase of recombination (t~250 s) is observed, attributed to additional conformational changes [3]. Differential FTIR bands of water associated with the QA/QA transition have been observed upon continuous illumination, leading to propose that weakly bound water molecules plays a role in P+QA stabilization [4]. By controlling the hydration level of RC-detergent films, through equilibration at given relative humidities (r), a strong inhibition of the P+QA conformational stabilization has been observed at low hydration [5]. We compared FTIR light-minus-dark (P+QA/ PQA) differential spectra in hydrated (r=76%) and dehydrated (r=11%) RC films over the 4000- 1000 cm-1. The spectra differ significantly in the 3750-3550 cm-1 range, the band attributed to weakly hydrogen bonded water molecules [5] being strongly reduced in the dried film. Dehydration also affects the 1800-1200 cm-1 range, which includes contributions from P, the quinones and the peptide. Optical absorption measurements performed under the same photoexcitation regime reveal a slow (t~5 s) kinetic component of P+QA recombination which disappears in the dehydrated sample, indicating at low r a destabilization of the charge separated state. As a whole the data suggest a correlation between the hydration shell dynamics and the conformational RC dynamics which stabilize the charge separated state.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
