The radius of gyration of a protein is a measure of its compactness. If a protein is stably folded, it will likely maintain a relatively steady value of R_g. If a protein unfolds, its R_g will change over time. Let's analyze the radius of gyration for lysozyme in our simulation:

gmx gyrate -s md_0_1.tpr -f md_0_1_noPBC.xtc -o gyrate.xvg

Choose group 1 (Protein) for analysis.

We can see from the reasonably invariant R_g values that the protein remains very stable, in its compact (folded) form over the course of 1 ns at 300 K. This result is not unexpected, but illustrates an advanced capacity of GROMACS analysis that comes built-in.