Effect of Near-Infrared Light on the S₂-State of the Manganese Complex of Photosystem II from Synechococcus elongatus

Abstract

The Mn cluster of Photosystem II (PSII) from Synechococcus elongatus was studied using EPR. A signal with features between g = 5 and g = 9 is reported from the S2-state. The signal is attributed to the manganese cluster in a state with a spin 5/2 state. Spectral simulations of the signal indicate zero field splitting parameters where the |E/D| was 0.13. The new signal is formed by irradiating PSII samples which contain the spin = 1/2 S2-state using 813 nm light below 200 K. This effect is attributed to a spin-state change in the manganese cluster due to absorption of the IR light by the Mn-cluster itself. The signal is similar to that reported recently in PSII of plants [Boussac, A., Un, S., Horner, O., and Rutherford, A. W. (1998) Biochemistry 37, 4001-4007]. In plant PSII the comparable signal is formed at a lower temperature (optimally below 77 K), and gradual warming of the sample in the dark leads to the formation of the state responsible for the well-known g = 4.1 signal prior to formation of the spin 1/2 multiline signal. In the present work using cyanobacterial PSII, warming of the sample in the dark leads to the formation of the spin 1/2 multiline signal without formation of the g = 4 type signal as an intermediate. These observations provide a partial explanation for the long-standing "mystery of the missing g = 4 state" in cyanobacterial PSII. The observations are rationalized in terms of three possible states which can exist for S2: (i) the spin 1/2 multiline signal, (ii) the state responsible for the g = 4.1 signal, and (iii) the new spin 5/2 state. The relative stability of these states differs between plants and cyanobacteria.

Towards Structural Determination of the Water-splitting Enzyme

“…37), our preparation contains all function relevant components of the electron donor and acceptor sides with highest degree of preservation. The isolated PS II shows the highest rate of oxygen evolution reported so far, which is in line with a clear multiline signal obtained from EPR measurements before, indicating a functional manganese cluster (38). High rates of oxygen evolution, up to 4500 M O 2 per mg of Chl and per hour, have also been reported from another PS II preparation of the same organism (41); however, this preparation still contains many contaminating proteins making it unsuitable for structural studies.…”

EPR spectroscopy of the manganese cluster of photosystem II

“…Since the g = 4.1 signal formed by near IR illumination relaxes back to the multiline signal at 200 K, the near IR component of broad light sources is not thought to be responsible for the g = 4.1 signal observed after illumination at 200 K. The near IR-induced conversion from multiline signal to g = 4.1 signal takes place via an intermediate S ‡ 5/2 spin state characterized by EPR signals at g = 6 and g = 10, which can be trapped by illumination at about 65 K (Boussac et al 1998b). Similar intermediate signals at g = 5-9 have been observed in cyanobacteria (Boussac et al 1998a), although the near IRinduced g = 4.1 signal has not.…”

“…Another previously observed Q-band signal, with features at about g = 4.3 and g = 4.1, was identified as the S 2 state g = 4.1 signal, leading to the suggestion that the signal arose from an S = 3/2 state (Smith et al 1993;Smith and Pace 1996); however, the identity of this signal has been called into question (Haddy et al 2004). The X-band g = 4.1 signal was thought not to form in cyanobacterial PSII (McDermott et al 1988;Boussac et al 1998a), however, it was recently shown that its presence correlates with the cytochrome c 550 (PsbV) content of the preparation (Lakshmi et al 2002).…”

Site-Directed Mutagenesis ofThermosynechococcus elongatusPhotosystem II: The O2-Evolving Enzyme Lacking the Redox-Active Tyrosine D

“…After the S 2 -multiline signal was recorded (spectrum c of Figure 8B), the sample was further illuminated by a 820-nm light at 50 K in the EPR cavity. This near-infrared illumination has been shown to convert the spin ) 1 / 2 S 2 -multiline signal state into an S g 5 / 2 spin state characterized by signals around g ) 9 in cyanobacteria (56). Spectrum d of Figure 8B is the difference signal of the before-minus-after 820-nm illumination and corresponds to the S 2 -multiline signal, which disappeared upon near-infrared illumination.…”