Wilk K E, Harrop S J, Jankova L, Edler D, Keenan G, Sharples F, Hiller R G, Curmi P M
Initiative in Biomolecular Structure, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
Proc Natl Acad Sci U S A. 1999 Aug 3;96(16):8901-6. doi: 10.1073/pnas.96.16.8901.
Cryptophytes are unicellular photosynthetic algae that use a lumenally located light-harvesting system, which is distinct from the phycobilisome structure found in cyanobacteria and red algae. One of the key components of this system is water-soluble phycoerythrin (PE) 545 whose expression is enhanced by low light levels. The crystal structure of the heterodimeric alpha(1)alpha(2)betabeta PE 545 from the marine cryptophyte Rhodomonas CS24 has been determined at 1.63-A resolution. Although the beta-chain structure is similar to the alpha and beta chains of other known phycobiliproteins, the overall structure of PE 545 is novel with the alpha chains forming a simple extended fold with an antiparallel beta-ribbon followed by an alpha-helix. The two doubly linked beta50/beta61 chromophores (one on each beta subunit) are in van der Waals contact, suggesting that exciton-coupling mechanisms may alter their spectral properties. Each alpha subunit carries a covalently linked 15,16-dihydrobiliverdin chromophore that is likely to be the final energy acceptor. The architecture of the heterodimer suggests that PE 545 may dock to an acceptor protein via a deep cleft and that energy may be transferred via this intermediary protein to the reaction center.
隐藻是单细胞光合藻类，其使用位于腔内的光捕获系统，该系统不同于蓝细菌和红藻中发现的藻胆体结构。该系统的关键组成部分之一是水溶性藻红蛋白（PE）545，其表达在低光照水平下会增强。已确定来自海洋隐藻红胞藻CS24的异源二聚体α(1)α(2)ββ PE 545的晶体结构，分辨率为1.63埃。虽然β链结构与其他已知藻胆蛋白的α链和β链相似，但PE 545的整体结构是新颖的，α链形成一个简单的延伸折叠结构，后面跟着一个反平行β带和一个α螺旋。两个双连接的β50/β61发色团（每个β亚基上一个）处于范德华接触，这表明激子耦合机制可能会改变它们的光谱特性。每个α亚基携带一个共价连接的15,16-二氢胆绿素发色团，它可能是最终的能量受体。异源二聚体的结构表明，PE 545可能通过一个深裂缝与受体蛋白对接，并且能量可能通过这个中间蛋白转移到反应中心。
