Department of Biochemistry and Molecular Biology, Life Sciences Bldg., University of Georgia, Athens, GA 30602-7229, USA.
J Bacteriol. 2011 Dec;193(23):6498-504. doi: 10.1128/JB.05445-11. Epub 2011 Sep 30.
Transcriptional and enzymatic analyses of Pyrococcus furiosus previously indicated that three proteins play key roles in the metabolism of elemental sulfur (S(0)): a membrane-bound oxidoreductase complex (MBX), a cytoplasmic coenzyme A-dependent NADPH sulfur oxidoreductase (NSR), and sulfur-induced protein A (SipA). Deletion strains, referred to as MBX1, NSR1, and SIP1, respectively, have now been constructed by homologous recombination utilizing the uracil auxotrophic COM1 parent strain (ΔpyrF). The growth of all three mutants on maltose was comparable without S(0), but in its presence, the growth of MBX1 was greatly impaired while the growth of NSR1 and SIP1 was largely unaffected. In the presence of S(0), MBX1 produced little, if any, sulfide but much more acetate (per unit of protein) than the parent strain, demonstrating that MBX plays a critical role in S(0) reduction and energy conservation. In contrast, comparable amounts of sulfide and acetate were produced by NSR1 and the parent strain, indicating that NSR is not essential for energy conservation during S(0) reduction. Differences in transcriptional responses to S(0) in NSR1 suggest that two sulfide dehydrogenase isoenzymes provide a compensatory NADPH-dependent S(0) reduction system. Genes controlled by the S(0)-responsive regulator SurR were not as highly regulated in MBX1 and NSR1. SIP1 produced the same amount of acetate but more sulfide than the parent strain. That SipA is not essential for growth on S(0) indicates that it is not required for detoxification of metal sulfides, as previously suggested. A model is proposed for S(0) reduction by P. furiosus with roles for MBX and NSR in bioenergetics and for SipA in iron-sulfur metabolism.
先前的转录和酶学分析表明,Pyrococcus furiosus 中有三种蛋白在元素硫(S(0))代谢中起着关键作用:一个膜结合氧化还原酶复合物(MBX)、细胞质辅酶 A 依赖的 NADPH 硫氧化还原酶(NSR)和硫诱导蛋白 A(SipA)。现在已经通过同源重组利用尿嘧啶营养缺陷型 COM1 亲本菌株(ΔpyrF)构建了分别称为 MBX1、NSR1 和 SIP1 的缺失菌株。在没有 S(0)的情况下,所有三种突变体在麦芽糖上的生长情况相当,但在存在 S(0)的情况下,MBX1 的生长受到严重损害,而 NSR1 和 SIP1 的生长基本不受影响。在 S(0)存在的情况下,MBX1 产生的硫化物很少(如果有的话),但比亲本菌株产生的乙酸盐多得多(每单位蛋白),这表明 MBX 在 S(0)还原和能量守恒中起着关键作用。相比之下,NSR1 和亲本菌株产生的硫化物和乙酸盐量相当,这表明 NSR 在 S(0)还原过程中不是能量守恒所必需的。NSR1 对 S(0)的转录响应差异表明两种硫化物脱氢酶同工酶提供了一个补偿 NADPH 依赖的 S(0)还原系统。受 S(0)响应调节因子 SurR 控制的基因在 MBX1 和 NSR1 中的调控程度不高。SIP1 产生的乙酸盐量与亲本菌株相同,但产生的硫化物量更多。SipA 对于在 S(0)上的生长不是必需的,这表明它不需要用于金属硫化物的解毒,正如之前所提出的。提出了一个 P. furiosus 还原 S(0)的模型,MBX 和 NSR 在生物能量学中起作用,SipA 在铁硫代谢中起作用。