engleski

Temperature-dependent structural changes in Cas3 protein in Escherichia coli

The CRSISPR-Cas system is a significant mechanism of bacteria and archea that provide adaptive immunity against viruses and plasmids. It consists of DNA repeats separated by spacers of foreign origin (CRISPR locus), and cas genes responsible for various stages of defense. In E. coli, Cas3 protein is involved in a degradation of invader DNA as a last stage of defense. Recent studies showed that Cas3 could be the limiting factor for regulation of the CRISPR-Cas immunity due to its unusual property – loss of activity at 37°C, unless the protein is present in abundance. In this work we wanted to investigate if the loss of Cas3 activity is caused by structural change of protein which is temperature-dependent. We monitored structural changes in the purified protein by measuring a change of ellipticity using circular dichroism and by measuring intrinsic tryptophan fluorescence using fluorescence spectrometry. Both methods gave the same result, a subtle conformational change in helical region at 35°C which is in agreement with the protein activity change in vivo. This is probably the first experimental evidence that Cas3 activity from E. coli is temperature-dependent due to the change in protein conformation. Also, similar structural change was observed in archaeal Cas3 suggesting that this trait is preserved in other species as well. The results of this research will contribute to better understanding of regulation of Cas3 activity as well as to the progress of the CRISPR-Cas field.

CRISPR-Cas ; Cas3 ; circular dichroism ; intrinsic tryptophan fluorescence ; E. coli

nije evidentirano