Hi Jacob, Interesting topic.
This reminds me the posters I saw on ACA 2010, on the femto-second infrared laser based instrument . That instrument utilizes the nonlinear optical properties of crystals of chiral molecules to detect very small crystalline materials from amorphous background: the crystals will double the frequency of the laser, turning the infrared light to visible light. I cannot recall the exact name of the technology now, unfortunately. Your case of observing in vivo GFP crystals is a little special in that the crystals are fluorescent. I guess if we scan cells over-expressing proteins with the above mentioned instrument, we might find that many proteins will do the same in cells. Naturally occurring in vivo crystals are not very rare. If we do not restrict the topic to proteins, then it is well known that many viruses readily crystallize in the host cell's nuclei and the resulting crystals or crystalline arrays can be observed under EM. And if we do not restrict the cells to mammalian cells, then there come the famous BT crystals. In addition, I just did some internet search and here are some interesting results: 1) Viral protein crystals can form in HEK cells infected by adenovirus (http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002894) 2) Bacterial infection can cause the infected epithelial cells to form pathological crystal-containing inclusion bodies in the cytosol (http://www.ncbi.nlm.nih.gov/pubmed/8940763). 3) Crystalline inclusion bodies are found in rabbit embryos (http://dev.biologists.org/content/44/1/31.full.pdf) and epididymis of the nine-banded armadillo(http://www.sciencedirect.com/science/article/pii/S0022532073800073). Actually if google "crystalline inclusion body", there will be tons of literatures. 4) IgG crystallized in the ER when over expressed from a highly optimized CHO expression system (http://www.jbc.org/content/286/22/19917.abstract). This is particularly interesting as we know that whole IgGs are not so prone to crystallize, although the author do state that "Crystallizing propensity was due to the intrinsic physicochemical properties of the model IgG". Given the prevalence of in vivo crystallization, especially considering their correlation with inclusion bodies, I think it is reasonable to suspect that there are some cases that the inclusion bodies formed during over expression of transgenic proteins in E. coli are crystalline. I expect that we will be enlightened on this issue by somebody on the BB soon. Zhijie From: Jacob Keller Sent: Friday, February 15, 2013 2:44 PM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] Sighting of Protein Crystals in Vivo?! Dear Crystallographers, I was looking at some live, control HEK cells expressing just eGFP, and to my great surprise, saw littered across the dish what appeared to be small fluorescent needles (see attached--sorry about the size, but it's only ~1MB total.) Can these possibly be fortuitous protein crystals? They were too small to mount I think, and for what it's worth, parallel-transfected HeLa cells did not have these things. But, some needles could be seen in the DIC images as well, and the needles were only fluorescent with GFP filter sets, and not CFP, YFP, or texas red filters. I thought of whale myoglobin crystallizing on the decks of ships, but never thought I would see this.... Jacob -- ******************************************* Jacob Pearson Keller, PhD Postdoctoral Associate HHMI Janelia Farms Research Campus email: j-kell...@northwestern.edu *******************************************
