Institute for Quantitative Biosciences (QB3), University of California, Berkeley, CA 94720.
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 2018 Nov 27;115(48):12206-12211. doi: 10.1073/pnas.1810517115. Epub 2018 Nov 8.
In vivo, proteins fold and function in a complex environment subject to many stresses that can modulate a protein's energy landscape. One aspect of the environment pertinent to protein folding is the ribosome, since proteins have the opportunity to fold while still bound to the ribosome during translation. We use a combination of force and chemical denaturant (chemomechanical unfolding), as well as point mutations, to characterize the folding mechanism of the src SH3 domain both as a stalled ribosome nascent chain and free in solution. Our results indicate that src SH3 folds through the same pathway on and off the ribosome. Molecular simulations also indicate that the ribosome does not affect the folding pathway for this small protein. Taken together, we conclude that the ribosome does not alter the folding mechanism of this small protein. These results, if general, suggest the ribosome may exert a bigger influence on the folding of multidomain proteins or protein domains that can partially fold before the entire domain sequence is outside the ribosome exit tunnel.
在体内，蛋白质在复杂的环境中折叠并发挥功能，这些环境会受到许多压力的影响，从而调节蛋白质的能量景观。与蛋白质折叠相关的环境方面之一是核糖体，因为在翻译过程中，蛋白质有机会在与核糖体结合的同时折叠。我们使用力和化学变性剂（化学机械展开）以及点突变的组合来表征 src SH3 结构域的折叠机制，既作为核糖体新生链上的停滞态，也作为游离于溶液中的状态。我们的结果表明，src SH3 在核糖体上和核糖体外通过相同的途径折叠。分子模拟也表明，核糖体不会影响这种小蛋白质的折叠途径。总之，我们得出结论，核糖体不会改变这种小蛋白质的折叠机制。如果这些结果具有普遍性，那么它们表明核糖体可能会对多结构域蛋白质或在整个结构域序列离开核糖体出口隧道之前可以部分折叠的蛋白质结构域的折叠产生更大的影响。
