在蛋白合成过程中,转移核糖核酸(转移RNA,即tRNA)在其所附着的氨基酸被转移到生长中的肽链之上时,依次通过核糖体的A点、P点和E点。大尺度的构形运动伴随着它们的转位。
Holger Stark及其同事对核糖体数量惊人的190万幅“单颗粒”冷电子显微图像进行了处理,以观察这些动态变化。他们得出结论说,构形变化是由热驱动的,或者说是“布朗运动”,所发生的变化引起tNRA在一个狭窄路径上穿过核糖体做定向运动。(生物谷Bioon.net)
生物谷推荐原文出处:
Nature doi:10.1038/nature09206
Ribosome dynamics and tRNA movement by time-resolved electron cryomicroscopy
Niels Fischer, Andrey L. Konevega, Wolfgang Wintermeyer, Marina V. Rodnina & Holger Stark
The translocation step of protein synthesis entails large-scale rearrangements of the ribosome–transfer RNA (tRNA) complex. Here we have followed tRNA movement through the ribosome during translocation by time-resolved single-particle electron cryomicroscopy (cryo-EM). Unbiased computational sorting of cryo-EM images yielded 50 distinct three-dimensional reconstructions, showing the tRNAs in classical, hybrid and various novel intermediate states that provide trajectories and kinetic information about tRNA movement through the ribosome. The structures indicate how tRNA movement is coupled with global and local conformational changes of the ribosome, in particular of the head and body of the small ribosomal subunit, and show that dynamic interactions between tRNAs and ribosomal residues confine the path of the tRNAs through the ribosome. The temperature dependence of ribosome dynamics reveals a surprisingly flat energy landscape of conformational variations at physiological temperature. The ribosome functions as a Brownian machine that couples spontaneous conformational changes driven by thermal energy to directed movement.