Cleaning protocols for crystallization robots: preventing protease contamination

摘要

The protease in the commonly used commercial low-foam enzyme cleaner Zymit cannot be completely blocked by EDTA, a widely used inhibitor of metalloproteases, at concentrations of up to 5mM. Severe protein degradation was observed in crystallization drops after EDTA-containing wash steps unless residual Zymit protease was removed with NaOH at a concentration of at least 0.1M. Wash steps with 0.1% SDS were also ineffective in completely removing the remaining Zymit activity. Protocols including wash steps with at least 0.1M NaOH, as for example specified in the original ZENM protocol, are recommended to completely deactivate Zymit protease activity.