Search

Biological [Fe-S] clusters are increasingly recognized to undergo proton-coupled electron transfer (PCET), but the site of protonation, mechanism, and role for PCET remains largely unknown. Here we explore this reactivity with synthetic model clusters. Protonation of the arylthiolate-ligated [4Fe-4S] cluster [Fe4 S4 (SAr)4 ](2-) (1, SAr=S-2,4-6-(iPr)3 C6 H2 ) leads to thiol dissociation, reversibly forming [Fe4 S4 (SAr)3 L](1-) (2) and ArSH (L=solvent, and/or conjugate base). Solutions of 2+ArSH react with the nitroxyl radical TEMPO to give [Fe4 S4 (SAr)4 ](1-) (1ox ) and TEMPOH. This reaction involves PCET coupled to thiolate association and may proceed via the unobserved protonated cluster [Fe4 S4 (SAr)3 (HSAr)](1-) (1-H). Similar reactions with this and related clusters proceed comparably. An understanding of the PCET thermochemistry of this cluster system has been developed, encompassing three different redox levels and two protonation states., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Biological [Fe-S] clusters are increasingly recognized to undergo proton-coupled electron transfer (PCET), but the site of protonation, mechanism, and role for PCET remains largely unknown. Here we explore this reactivity with synthetic model clusters. Protonation of the arylthiolate-ligated [4Fe-4S] cluster [Fe4S4(SAr)4]2− ( 1, SAr=S-2,4-6-( iPr)3C6H2) leads to thiol dissociation, reversibly forming [Fe4S4(SAr)3L]1− ( 2) and ArSH (L=solvent, and/or conjugate base). Solutions of 2+ArSH react with the nitroxyl radical TEMPO to give [Fe4S4(SAr)4]1− ( 1ox) and TEMPOH. This reaction involves PCET coupled to thiolate association and may proceed via the unobserved protonated cluster [Fe4S4(SAr)3(HSAr)]1− ( 1-H). Similar reactions with this and related clusters proceed comparably. An understanding of the PCET thermochemistry of this cluster system has been developed, encompassing three different redox levels and two protonation states. [ABSTRACT FROM AUTHOR]

Abstract: The plastid of Plasmodium falciparum, the apicoplast, performs metabolic functions essential to the parasite. Various reactions in the plastid require the assembly of [Fe–S] prosthetic groups on participating proteins as well as the reductant activity of ferredoxin that is converted from its apo-form by the assembly of [Fe–S] clusters inside the apicoplast. The [Fe–S] assembly pathway involving sulphur mobilising Suf proteins has been predicted to function in the apicoplast with one component (PfSufB) encoded by the plastid genome itself. We demonstrate the ATPase activity of recombinant P. falciparum nuclear-encoded SufC and its localisation in the apicoplast. Further, an internal region of apicoplast SufB was used to detect PfSufB–PfSufC interaction in vitro; co-elution of SufB from parasite lysate with recombinant PfSufC on an affinity column also indicated an interaction of the two proteins. As a departure from bacterial SufB and similar to reported plant plastid SufB, apicoplast SufB exhibited ATPase activity, suggesting the evolution of specialised functions in the plastid counterparts. Our results provide experimental evidence for an active Suf pathway in the Plasmodium apicoplast. [Copyright &y& Elsevier]