Calcium controls the assembly of the photosynthetic water-oxidizing complex:: a cadmium(II) inorganic mutant of the Mn4Ca core

被引:18
作者
Bartlett, John E. [1 ,2 ]
Baranov, Sergei V. [1 ,2 ]
Ananyev, Gennady M. [1 ,2 ]
Dismukes, G. Charles [1 ,2 ]
机构
[1] Princeton Univ, Dept Chem, Princeton, NJ 08544 USA
[2] Princeton Univ, Inst Environm, Princeton, NJ 08544 USA
关键词
calcium; manganese; oxygen evolution; photosystem II; photosynthesis; water oxidation;
D O I
10.1098/rstb.2007.2222
中图分类号
Q [生物科学];
学科分类号
07 ; 0710 ; 09 ;
摘要
Perturbation of the catalytic inorganic core (Mn4Ca1OxCly) of the photosystem II-water-oxidizing complex (PSII-WOC) isolated from spinach is examined by substitution of Ca2+ with cadmium(II) during core assembly. Cd2+ inhibits the yield of reconstitution of O-2-evolution activity, called photoactivation, starting from the free inorganic cofactors and the cofactor-depleted apo-WOC-PSII complex. Ca2+ affinity increases following photooxidation of the first Mn2+ to Mn3+ bound to the 'high-affinity' site. Ca2+ binding occurs in the dark and is the slowest overall step of photoactivation (IM1/IM*(1) -> step). Cd2+ competitively blocks the binding of Ca2+ to its functional site with 10-to 30-fold higher affinity, but does not influence the binding of Mn2+ to its high-affinity site. By contrast, even 10-fold higher concentrations of Cd2+ have no effect on O-2-evolution activity in intact PSII-WOC. Paradoxically, Cd2+ both inhibits photoactivation yield, while accelerating the rate of photoassembly of active centres 10-fold relative to Ca2+. Cd2+ increases the kinetic stability of the photooxidized Mn3+ assembly intermediate(s) by twofold (mean lifetime for dark decay). The rate data provide evidence that Cd2+ binding following photooxidation of the first Mn3+, IM1/IM*(1), causes three outcomes: (i) a longer intermediate lifetime that slows IM1 decay to IM0 by charge recombination, (ii) 10-fold higher probability of attaining the degrees of freedom (either or both cofactor and protein d.f.) needed to bind and photooxidize the remaining 3 Mn2+ that form the functional cluster, and (iii) increased lability of Cd2+ following Mn-4 cluster assembly results in (re) exchange of Cd2+ by Ca2+ which restores active O-2-evolving centres. Prior EPR spectroscopic data provide evidence for an oxo-bridged assembly intermediate, Mn3+ (mu-O2-) Ca2+, for IM*(1). We postulate an analogous inhibited intermediate with Cd2+ replacing Ca2+.
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页码:1253 / 1261
页数:9
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