ABSTRACT
Integral membrane protein complexes consisting of proteins and small molecules that act as cofactors have important functions in all organisms. To form functional complexes, cofactor biosynthesis must be coordinated with the production of corresponding apoproteins. To examine this coordination, we study bacteriorhodopsin (BR), a light-induced proton pump in the halophilic archaeon
Halobacterium salinarum
. This complex consists of a retinal cofactor and bacterioopsin (BO), the BR apoprotein. To examine possible novel regulatory mechanisms linking BO and retinal biosynthesis, we deleted
bop
, the gene that encodes BO.
bop
deletion resulted in a dramatic increase of bacterioruberins, carotenoid molecules that share biosynthetic precursors with retinal. Additional studies revealed that bacterioruberins accumulate in the absence of BO regardless of the presence of retinal or BR, suggesting that BO inhibits bacterioruberin biosynthesis to increase the availability of carotenoid precursors for retinal biosynthesis. To further examine this potential regulatory mechanism, we characterized an enzyme, encoded by the
lye
gene, that catalyzes bacterioruberin biosynthesis. BO-mediated inhibition of bacterioruberin synthesis appears to be specific to the
H. salinarum
lye
-encoded enzyme, as expression of a
lye
homolog from
Haloferax volcanii
, a related archaeon that synthesizes bacterioruberins but lacks opsins, resulted in bacterioruberin synthesis that was not reduced in the presence of BO. Our results provide evidence for a novel regulatory mechanism in which biosynthesis of a cofactor is promoted by apoprotein-mediated inhibition of an alternate biochemical pathway. Specifically, BO accumulation promotes retinal production by inhibiting bacterioruberin biosynthesis.
摘要
由作为辅助因子的蛋白质和小分子组成的整体膜蛋白复合物在所有
生物体中都具有重要功能。要形成功能性复合物,辅助因子的
生物合成必须与相应的载体蛋白的生成相协调。为了研究这种协调,我们研究了嗜盐古细菌中的一种光诱导质子泵--bacteriorhodopsin(BR)。
盐生卤杆菌
.该复合物由视网膜辅助因子和细菌
核糖体蛋白(BR)组成。为了研究可能将 BO 和视网膜
生物合成联系起来的新型调控机制,我们删除了
bop
的
基因。
bop
基因缺失会导致类
胡萝卜素分子--细菌小檗素--的急剧增加,而细菌小檗素与视网膜具有相同的
生物合成前体。其他研究表明,无论视网膜或 BR 存在与否,细菌
前胡素都会在没有 BO 的情况下积累,这表明 BO 会抑制细菌
前胡素的
生物合成,以增加视网膜
生物合成所需的类
胡萝卜素前体。为了进一步研究这种潜在的调控机制,我们鉴定了一种由
碱液
基因编码的一种酶的特征。由 BO 介导的对细菌
奥曲肽合成的抑制似乎对
盐渍菌
碱液
-编码的酶具有特异性。
碱液
同源物
的碱液同源物
的碱液同源物,这种同源物能合成细菌绿蛋白但缺乏
蛋白酶。我们的研究结果为一种新的调控机制提供了证据,在这种机制中,辅助因子的
生物合成是由
载脂蛋白介导的对另一种生化途径的抑制所促进的。具体来说,BO 的积累通过抑制细菌小檗素的
生物合成来促进视网膜的生成。