Moreover, mutation D114C might result in a lower conformational entropy of the amino acid side chains at position 114, which would also contribute to improved protein crystallization. After crystallization of HheG wild type and D114C at 20 µl scale, cross-linking of both variants with the cysteine-specific cross-linker BMOE was tested. As expected, crystals of HheG wild type incubated with 2 mM BMOE for 24 h re-dissolved within 72 h after transfer into reaction buffer (Figure ). In contrast, respective crystals of HheG D114C did not re-dissolve after cross-linking with 2 mM BMOE for 24 h (Figure ). This indicates that only HheG D114C crystals offer suitable cross-linking sites for stable cross-linking with BMOE.